Index: Ringtoets/Common/src/Ringtoets.Common.Data/FailureMechanism/FailureMechanismSectionCollection.cs
===================================================================
diff -u -rd507de965210c6af40d57936780fa55b05430e13 -r2c6d254976145b223c6055b0b8c0c8303f8038a1
--- Ringtoets/Common/src/Ringtoets.Common.Data/FailureMechanism/FailureMechanismSectionCollection.cs	(.../FailureMechanismSectionCollection.cs)	(revision d507de965210c6af40d57936780fa55b05430e13)
+++ Ringtoets/Common/src/Ringtoets.Common.Data/FailureMechanism/FailureMechanismSectionCollection.cs	(.../FailureMechanismSectionCollection.cs)	(revision 2c6d254976145b223c6055b0b8c0c8303f8038a1)
@@ -29,6 +29,9 @@
 
 namespace Ringtoets.Common.Data.FailureMechanism
 {
+    /// <summary>
+    /// A collection of <see cref="FailureMechanismSection"/>.
+    /// </summary>
     public class FailureMechanismSectionCollection : Observable, IEnumerable<FailureMechanismSection>
     {
         private readonly List<FailureMechanismSection> sections = new List<FailureMechanismSection>();
@@ -50,12 +53,16 @@
         }
 
         /// <summary>
-        /// Adds all <see cref="FailureMechanismSection"/> originating from a source file.
+        /// Sets all <see cref="FailureMechanismSection"/> originating from a source file to the collection.
         /// </summary>
-        /// <param name="failureMechanismSections">The collection of <see cref="FailureMechanismSection"/> to add</param>
+        /// <param name="failureMechanismSections">The collection of <see cref="FailureMechanismSection"/> to set.</param>
         /// <param name="sourcePath">The path to the source file.</param>
         /// <exception cref="ArgumentNullException">Thrown when any parameter is <c>null</c>.</exception>
-        /// <exception cref="ArgumentException">Thrown when <paramref name="sourcePath"/> is not a valid file path.</exception>
+        /// <exception cref="ArgumentException">Thrown when:
+        /// <list type="bullet">
+        /// <item><paramref name="sourcePath"/> is not a valid file path.</item>
+        /// <item><paramref name="failureMechanismSections"/> contains sections that are not properly chained.</item>
+        /// </list></exception>
         public void SetSections(IEnumerable<FailureMechanismSection> failureMechanismSections,
                                 string sourcePath)
         {
@@ -74,27 +81,29 @@
                 throw new ArgumentException($@"'{sourcePath}' is not a valid file path.", nameof(sourcePath));
             }
 
-            Clear();
+            if (!failureMechanismSections.Any())
+            {
+                Clear();
+                SourcePath = sourcePath;
+                return;
+            }
 
-            if (failureMechanismSections.Any())
+            FailureMechanismSection firstSection = failureMechanismSections.First();
+            var newSections = new List<FailureMechanismSection>
             {
-                FailureMechanismSection firstSection = failureMechanismSections.First();
-                var newSections = new List<FailureMechanismSection>
-                {
-                    firstSection
-                };
+                firstSection
+            };
 
-                FailureMechanismSection previousSection = firstSection;
-                foreach (FailureMechanismSection section in failureMechanismSections.Skip(1))
-                {
-                    ValidateSection(section, previousSection);
-                    newSections.Add(section);
-                    previousSection = section;
-                }
-
-                sections.AddRange(newSections);
+            FailureMechanismSection previousSection = firstSection;
+            foreach (FailureMechanismSection section in failureMechanismSections.Skip(1))
+            {
+                ValidateSection(section, previousSection);
+                newSections.Add(section);
+                previousSection = section;
             }
 
+            Clear();
+            sections.AddRange(newSections);
             SourcePath = sourcePath;
         }
 
Index: Ringtoets/Common/src/Ringtoets.Common.Data/FailureMechanism/IFailureMechanism.cs
===================================================================
diff -u -r88ba44b92caad86cf1343d9c191bc22761463c8c -r2c6d254976145b223c6055b0b8c0c8303f8038a1
--- Ringtoets/Common/src/Ringtoets.Common.Data/FailureMechanism/IFailureMechanism.cs	(.../IFailureMechanism.cs)	(revision 88ba44b92caad86cf1343d9c191bc22761463c8c)
+++ Ringtoets/Common/src/Ringtoets.Common.Data/FailureMechanism/IFailureMechanism.cs	(.../IFailureMechanism.cs)	(revision 2c6d254976145b223c6055b0b8c0c8303f8038a1)
@@ -96,8 +96,11 @@
         /// <param name="sections">The sections to set.</param>
         /// <param name="sourcePath">The path of the file the sections originate from.</param>
         /// <exception cref="ArgumentNullException">Thrown when any parameter is <c>null</c>.</exception>
-        /// <exception cref="ArgumentException">Thrown when <paramref name="sections"/> cannot
-        /// be connected to elements already defined in <see cref="Sections"/>.</exception>
+        /// <exception cref="ArgumentException">Thrown when:
+        /// <list type="bullet">
+        /// <item><paramref name="sourcePath"/> is not a valid file path.</item>
+        /// <item><paramref name="sections"/> contains sections that are not properly chained.</item>
+        /// </list></exception>
         void SetSections(IEnumerable<FailureMechanismSection> sections, string sourcePath);
 
         /// <summary>
Index: Ringtoets/Common/test/Ringtoets.Common.Data.Test/FailureMechanism/FailureMechanismBaseTest.cs
===================================================================
diff -u -ra100a49622ba13deb720c2c881906e890cb8094e -r2c6d254976145b223c6055b0b8c0c8303f8038a1
--- Ringtoets/Common/test/Ringtoets.Common.Data.Test/FailureMechanism/FailureMechanismBaseTest.cs	(.../FailureMechanismBaseTest.cs)	(revision a100a49622ba13deb720c2c881906e890cb8094e)
+++ Ringtoets/Common/test/Ringtoets.Common.Data.Test/FailureMechanism/FailureMechanismBaseTest.cs	(.../FailureMechanismBaseTest.cs)	(revision 2c6d254976145b223c6055b0b8c0c8303f8038a1)
@@ -274,11 +274,15 @@
             });
 
             var failureMechanism = new SimpleFailureMechanismBase();
+            string sourcePath = TestHelper.GetScratchPadPath();
             failureMechanism.SetSections(new[]
             {
                 section
-            }, string.Empty);
+            }, sourcePath);
 
+            // Precondition
+            Assert.AreEqual(sourcePath, failureMechanism.FailureMechanismSectionSourcePath);
+
             // Call
             failureMechanism.ClearAllSections();
 
Index: Ringtoets/Common/test/Ringtoets.Common.Data.Test/FailureMechanism/FailureMechanismSectionCollectionTest.cs
===================================================================
diff -u -rd507de965210c6af40d57936780fa55b05430e13 -r2c6d254976145b223c6055b0b8c0c8303f8038a1
--- Ringtoets/Common/test/Ringtoets.Common.Data.Test/FailureMechanism/FailureMechanismSectionCollectionTest.cs	(.../FailureMechanismSectionCollectionTest.cs)	(revision d507de965210c6af40d57936780fa55b05430e13)
+++ Ringtoets/Common/test/Ringtoets.Common.Data.Test/FailureMechanism/FailureMechanismSectionCollectionTest.cs	(.../FailureMechanismSectionCollectionTest.cs)	(revision 2c6d254976145b223c6055b0b8c0c8303f8038a1)
@@ -143,10 +143,15 @@
         }
 
         [Test]
-        public void SetSections_SecondSectionDoesNotConnectToFirst_ThrowsArgumentExceptionAndDoesNotSetSections()
+        public void SetSections_SecondSectionDoesNotConnectToFirst_ThrowsArgumentExceptionAndOldDataRemains()
         {
             // Setup
             var sectionCollection = new FailureMechanismSectionCollection();
+            string oldPath = TestHelper.GetScratchPadPath();
+            sectionCollection.SetSections(new[]
+            {
+                FailureMechanismSectionTestFactory.CreateFailureMechanismSection()
+            }, oldPath);
 
             var section1 = new FailureMechanismSection("A", new[]
             {
@@ -169,8 +174,8 @@
             // Assert
             const string expectedMessage = "Vak 'B' sluit niet aan op de al gedefinieerde vakken van het toetsspoor.";
             TestHelper.AssertThrowsArgumentExceptionAndTestMessage<ArgumentException>(call, expectedMessage);
-            CollectionAssert.IsEmpty(sectionCollection);
-            Assert.IsNull(sectionCollection.SourcePath);
+            Assert.AreEqual(1, sectionCollection.Count());
+            Assert.AreEqual(oldPath, sectionCollection.SourcePath);
         }
 
         [Test]
Index: Ringtoets/Common/test/Ringtoets.Common.Data.TestUtil.Test/FailureMechanismTestHelperTest.cs
===================================================================
diff -u -rd2efd1dfcfbd8f09a47533950d3e89474ae2e1af -r2c6d254976145b223c6055b0b8c0c8303f8038a1
--- Ringtoets/Common/test/Ringtoets.Common.Data.TestUtil.Test/FailureMechanismTestHelperTest.cs	(.../FailureMechanismTestHelperTest.cs)	(revision d2efd1dfcfbd8f09a47533950d3e89474ae2e1af)
+++ Ringtoets/Common/test/Ringtoets.Common.Data.TestUtil.Test/FailureMechanismTestHelperTest.cs	(.../FailureMechanismTestHelperTest.cs)	(revision 2c6d254976145b223c6055b0b8c0c8303f8038a1)
@@ -44,7 +44,7 @@
 
             // Assert
             Assert.IsEmpty(failureMechanism.FailureMechanismSectionSourcePath);
-            Assert.AreEqual(sections.Single(), failureMechanism.Sections.Single());
+            Assert.AreSame(sections.Single(), failureMechanism.Sections.Single());
         }
     }
 }
\ No newline at end of file
Index: Ringtoets/Common/test/Ringtoets.Common.Data.TestUtil/FailureMechanismTestHelper.cs
===================================================================
diff -u -r235521fa82576e7717d74048522447a0e893af9a -r2c6d254976145b223c6055b0b8c0c8303f8038a1
--- Ringtoets/Common/test/Ringtoets.Common.Data.TestUtil/FailureMechanismTestHelper.cs	(.../FailureMechanismTestHelper.cs)	(revision 235521fa82576e7717d74048522447a0e893af9a)
+++ Ringtoets/Common/test/Ringtoets.Common.Data.TestUtil/FailureMechanismTestHelper.cs	(.../FailureMechanismTestHelper.cs)	(revision 2c6d254976145b223c6055b0b8c0c8303f8038a1)
@@ -37,8 +37,8 @@
         /// <param name="failureMechanism">The failure mechanism to set the sections to.</param>
         /// <param name="sections">The sections to set.</param>
         /// <exception cref="ArgumentNullException">Thrown when <see cref="sections"/> is <c>null</c>.</exception>
-        /// <exception cref="ArgumentException">Thrown when <paramref name="sections"/> cannot
-        /// be connected to elements already defined in <see cref="IFailureMechanism.Sections"/>.</exception>
+        /// <exception cref="ArgumentException">Thrown when <paramref name="sections"/> contains elements that
+        /// are not properly connected.</exception>
         public static void SetSections(IFailureMechanism failureMechanism, IEnumerable<FailureMechanismSection> sections)
         {
             failureMechanism.SetSections(sections, string.Empty);
Index: Ringtoets/Common/test/Ringtoets.Common.IO.Test/FileImporters/FailureMechanismSectionsImporterTest.cs
===================================================================
diff -u -r603210e73c97c052ba7fc2447b45cf57750a6ae4 -r2c6d254976145b223c6055b0b8c0c8303f8038a1
--- Ringtoets/Common/test/Ringtoets.Common.IO.Test/FileImporters/FailureMechanismSectionsImporterTest.cs	(.../FailureMechanismSectionsImporterTest.cs)	(revision 603210e73c97c052ba7fc2447b45cf57750a6ae4)
+++ Ringtoets/Common/test/Ringtoets.Common.IO.Test/FileImporters/FailureMechanismSectionsImporterTest.cs	(.../FailureMechanismSectionsImporterTest.cs)	(revision 2c6d254976145b223c6055b0b8c0c8303f8038a1)
@@ -169,9 +169,10 @@
             ReferenceLine importReferenceLine = ImportReferenceLine(referenceLineFilePath);
 
             var failureMechanism = new TestFailureMechanism();
+            var oldSection = new FailureMechanismSection("A", importReferenceLine.Points);
             FailureMechanismTestHelper.SetSections(failureMechanism, new[]
             {
-                new FailureMechanismSection("A", importReferenceLine.Points)
+                oldSection
             });
             var updateStrategy = new TestFailureMechanismSectionUpdateStrategy();
 
@@ -184,6 +185,7 @@
             Assert.IsTrue(importSuccessful);
 
             IEnumerable<FailureMechanismSection> sections = updateStrategy.ImportedFailureMechanismSections;
+            CollectionAssert.DoesNotContain(sections, oldSection);
             Assert.AreEqual(62, sections.Count());
             AssertSectionsAreValidForReferenceLine(sections, importReferenceLine);
             mocks.VerifyAll();
Index: Ringtoets/Integration/test/Ringtoets.Integration.Plugin.Test/TreeNodeInfos/FailureMechanismContextTreeNodeInfoTest.cs
===================================================================
diff -u -r9d464742b12df2c1a1779e74b8e289eed5045e91 -r2c6d254976145b223c6055b0b8c0c8303f8038a1
--- Ringtoets/Integration/test/Ringtoets.Integration.Plugin.Test/TreeNodeInfos/FailureMechanismContextTreeNodeInfoTest.cs	(.../FailureMechanismContextTreeNodeInfoTest.cs)	(revision 9d464742b12df2c1a1779e74b8e289eed5045e91)
+++ Ringtoets/Integration/test/Ringtoets.Integration.Plugin.Test/TreeNodeInfos/FailureMechanismContextTreeNodeInfoTest.cs	(.../FailureMechanismContextTreeNodeInfoTest.cs)	(revision 2c6d254976145b223c6055b0b8c0c8303f8038a1)
@@ -238,11 +238,7 @@
                 {
                     IsRelevant = false
                 };
-                FailureMechanismTestHelper.SetSections(failureMechanism, new [] {new FailureMechanismSection("A", new[]
-                {
-                    new Point2D(1, 2),
-                    new Point2D(5, 6)
-                })});
+
                 var failureMechanismContext = new FailureMechanismContext<IFailureMechanism>(failureMechanism, assessmentSection);
 
                 // Call
@@ -498,10 +494,10 @@
                 TreeNodeInfo info = GetInfo(plugin);
 
                 var failureMechanism = mocks.StrictMultiMock<IHasSectionResults<T>>(typeof(IFailureMechanism));
-                failureMechanism.Expect(fm => ((IFailureMechanism) fm).IsRelevant).Return(true);
+                failureMechanism.Expect(fm => fm.IsRelevant).Return(true);
                 failureMechanism.Expect(fm => fm.SectionResults).Return(new ObservableList<T>()).Repeat.Any();
-                failureMechanism.Expect(fm => ((IFailureMechanism) fm).InputComments).Return(new Comment());
-                failureMechanism.Expect(fm => ((IFailureMechanism) fm).OutputComments).Return(new Comment());
+                failureMechanism.Expect(fm => fm.InputComments).Return(new Comment());
+                failureMechanism.Expect(fm => fm.OutputComments).Return(new Comment());
                 var failureMechanismContext = mocks.Stub<FailureMechanismContext<IFailureMechanism>>(failureMechanism, assessmentSection);
 
                 mocks.ReplayAll();
Index: Ringtoets/Integration/test/Ringtoets.Integration.Plugin.Test/TreeNodeInfos/MacroStabilityOutwardsFailureMechanismContextTreeNodeInfoTest.cs
===================================================================
diff -u -r9d464742b12df2c1a1779e74b8e289eed5045e91 -r2c6d254976145b223c6055b0b8c0c8303f8038a1
--- Ringtoets/Integration/test/Ringtoets.Integration.Plugin.Test/TreeNodeInfos/MacroStabilityOutwardsFailureMechanismContextTreeNodeInfoTest.cs	(.../MacroStabilityOutwardsFailureMechanismContextTreeNodeInfoTest.cs)	(revision 9d464742b12df2c1a1779e74b8e289eed5045e91)
+++ Ringtoets/Integration/test/Ringtoets.Integration.Plugin.Test/TreeNodeInfos/MacroStabilityOutwardsFailureMechanismContextTreeNodeInfoTest.cs	(.../MacroStabilityOutwardsFailureMechanismContextTreeNodeInfoTest.cs)	(revision 2c6d254976145b223c6055b0b8c0c8303f8038a1)
@@ -214,14 +214,7 @@
             {
                 IsRelevant = false
             };
-            FailureMechanismTestHelper.SetSections(failureMechanism, new[]
-            {
-                new FailureMechanismSection("A", new[]
-                {
-                    new Point2D(1, 2),
-                    new Point2D(5, 6)
-                })
-            });
+
             var failureMechanismContext = new MacroStabilityOutwardsFailureMechanismContext(failureMechanism, assessmentSection);
 
             // Call
Index: Ringtoets/Integration/test/Ringtoets.Integration.Plugin.Test/TreeNodeInfos/PipingStructureFailureMechanismContextTreeNodeInfoTest.cs
===================================================================
diff -u -r9d464742b12df2c1a1779e74b8e289eed5045e91 -r2c6d254976145b223c6055b0b8c0c8303f8038a1
--- Ringtoets/Integration/test/Ringtoets.Integration.Plugin.Test/TreeNodeInfos/PipingStructureFailureMechanismContextTreeNodeInfoTest.cs	(.../PipingStructureFailureMechanismContextTreeNodeInfoTest.cs)	(revision 9d464742b12df2c1a1779e74b8e289eed5045e91)
+++ Ringtoets/Integration/test/Ringtoets.Integration.Plugin.Test/TreeNodeInfos/PipingStructureFailureMechanismContextTreeNodeInfoTest.cs	(.../PipingStructureFailureMechanismContextTreeNodeInfoTest.cs)	(revision 2c6d254976145b223c6055b0b8c0c8303f8038a1)
@@ -210,14 +210,7 @@
             {
                 IsRelevant = false
             };
-            FailureMechanismTestHelper.SetSections(failureMechanism, new[]
-            {
-                new FailureMechanismSection("A", new[]
-                {
-                    new Point2D(1, 2),
-                    new Point2D(5, 6)
-                })
-            });
+
             var failureMechanismContext = new PipingStructureFailureMechanismContext(failureMechanism, assessmentSection);
 
             // Call
Index: Ringtoets/MacroStabilityInwards/test/Ringtoets.MacroStabilityInwards.Forms.Test/Views/MacroStabilityInwardsCalculationsViewTest.cs
===================================================================
diff -u -r0d301f769dc84d57979a55d902c498afe5d93e19 -r2c6d254976145b223c6055b0b8c0c8303f8038a1
--- Ringtoets/MacroStabilityInwards/test/Ringtoets.MacroStabilityInwards.Forms.Test/Views/MacroStabilityInwardsCalculationsViewTest.cs	(.../MacroStabilityInwardsCalculationsViewTest.cs)	(revision 0d301f769dc84d57979a55d902c498afe5d93e19)
+++ Ringtoets/MacroStabilityInwards/test/Ringtoets.MacroStabilityInwards.Forms.Test/Views/MacroStabilityInwardsCalculationsViewTest.cs	(.../MacroStabilityInwardsCalculationsViewTest.cs)	(revision 2c6d254976145b223c6055b0b8c0c8303f8038a1)
@@ -1340,20 +1340,20 @@
             });
 
             var failureMechanism = new MacroStabilityInwardsFailureMechanism();
-            const string arbitrary = "path";
+            const string sourcePath = "path";
             failureMechanism.SurfaceLines.AddRange(new[]
             {
                 surfaceLine1,
                 surfaceLine2
-            }, arbitrary);
+            }, sourcePath);
             failureMechanism.StochasticSoilModels.AddRange(new[]
             {
                 MacroStabilityInwardsStochasticSoilModelTestFactory.CreateValidStochasticSoilModel("name", new[]
                 {
                     new Point2D(0.0, 0.0),
                     new Point2D(5.0, 0.0)
                 })
-            }, arbitrary);
+            }, sourcePath);
 
             FailureMechanismTestHelper.SetSections(failureMechanism, new[]
             {
Index: Ringtoets/MacroStabilityInwards/test/Ringtoets.MacroStabilityInwards.Plugin.Test/TreeNodeInfos/MacroStabilityInwardsFailureMechanismContextTreeNodeInfoTest.cs
===================================================================
diff -u -r6bc9f77c55e1fba2e86203b22778f8a405aee2eb -r2c6d254976145b223c6055b0b8c0c8303f8038a1
--- Ringtoets/MacroStabilityInwards/test/Ringtoets.MacroStabilityInwards.Plugin.Test/TreeNodeInfos/MacroStabilityInwardsFailureMechanismContextTreeNodeInfoTest.cs	(.../MacroStabilityInwardsFailureMechanismContextTreeNodeInfoTest.cs)	(revision 6bc9f77c55e1fba2e86203b22778f8a405aee2eb)
+++ Ringtoets/MacroStabilityInwards/test/Ringtoets.MacroStabilityInwards.Plugin.Test/TreeNodeInfos/MacroStabilityInwardsFailureMechanismContextTreeNodeInfoTest.cs	(.../MacroStabilityInwardsFailureMechanismContextTreeNodeInfoTest.cs)	(revision 2c6d254976145b223c6055b0b8c0c8303f8038a1)
@@ -214,8 +214,6 @@
             {
                 IsRelevant = false
             };
-            failureMechanism.CalculationsGroup.Children.Add(new MacroStabilityInwardsCalculationScenario());
-            failureMechanism.CalculationsGroup.Children.Add(new MacroStabilityInwardsCalculationScenario());
 
             var failureMechanismContext = new MacroStabilityInwardsFailureMechanismContext(failureMechanism, assessmentSection);
 
Index: Ringtoets/Piping/test/Ringtoets.Piping.Plugin.Test/TreeNodeInfos/PipingFailureMechanismContextTreeNodeInfoTest.cs
===================================================================
diff -u -r9395ef9c44963521a3d8a81cda0a040e7d08c589 -r2c6d254976145b223c6055b0b8c0c8303f8038a1
--- Ringtoets/Piping/test/Ringtoets.Piping.Plugin.Test/TreeNodeInfos/PipingFailureMechanismContextTreeNodeInfoTest.cs	(.../PipingFailureMechanismContextTreeNodeInfoTest.cs)	(revision 9395ef9c44963521a3d8a81cda0a040e7d08c589)
+++ Ringtoets/Piping/test/Ringtoets.Piping.Plugin.Test/TreeNodeInfos/PipingFailureMechanismContextTreeNodeInfoTest.cs	(.../PipingFailureMechanismContextTreeNodeInfoTest.cs)	(revision 2c6d254976145b223c6055b0b8c0c8303f8038a1)
@@ -210,13 +210,10 @@
             var assessmentSection = mocks.Stub<IAssessmentSection>();
             mocks.ReplayAll();
 
-            var generalInputParameters = new GeneralPipingInput();
             var pipingFailureMechanism = new PipingFailureMechanism
             {
                 IsRelevant = false
             };
-            pipingFailureMechanism.CalculationsGroup.Children.Add(new PipingCalculationScenario(generalInputParameters));
-            pipingFailureMechanism.CalculationsGroup.Children.Add(new PipingCalculationScenario(generalInputParameters));
 
             var pipingFailureMechanismContext = new PipingFailureMechanismContext(pipingFailureMechanism, assessmentSection);