Index: Ringtoets/Integration/src/Ringtoets.Integration.Plugin/Merge/AssessmentSectionMergeHandler.cs
===================================================================
diff -u -r840f6ddca0edcb0e0effd1567df7291367d339cb -r8536b5bd3d91298dc866db708d7c75ae10fc84de
--- Ringtoets/Integration/src/Ringtoets.Integration.Plugin/Merge/AssessmentSectionMergeHandler.cs	(.../AssessmentSectionMergeHandler.cs)	(revision 840f6ddca0edcb0e0effd1567df7291367d339cb)
+++ Ringtoets/Integration/src/Ringtoets.Integration.Plugin/Merge/AssessmentSectionMergeHandler.cs	(.../AssessmentSectionMergeHandler.cs)	(revision 8536b5bd3d91298dc866db708d7c75ae10fc84de)
@@ -24,6 +24,7 @@
 using System.Linq;
 using Core.Common.Base;
 using Core.Common.Gui.Commands;
+using Core.Common.Util.Extensions;
 using log4net;
 using Ringtoets.ClosingStructures.Data;
 using Ringtoets.Common.Data.AssessmentSection;
@@ -92,47 +93,58 @@
             }
 
             BeforeMerge(targetAssessmentSection);
-            MergeHydraulicBoundaryLocations(targetAssessmentSection, sourceAssessmentSection);
+
+            var changedObjects = new List<IObservable>
+            {
+                targetAssessmentSection
+            };
+
+            changedObjects.AddRange(MergeHydraulicBoundaryLocations(targetAssessmentSection, sourceAssessmentSection));
             MergeFailureMechanisms(targetAssessmentSection, failureMechanismsToMerge);
-            AfterMerge(targetAssessmentSection);
+
+            AfterMerge(changedObjects);
         }
 
         private void BeforeMerge(AssessmentSection assessmentSection)
         {
             viewCommands.RemoveAllViewsForItem(assessmentSection);
         }
 
-        private static void AfterMerge(AssessmentSection targetAssessmentSection)
+        private static void AfterMerge(IEnumerable<IObservable> changedObjects)
         {
-            targetAssessmentSection.NotifyObservers();
+            changedObjects.ForEachElementDo(co => co.NotifyObservers());
         }
 
         #region HydraulicBoundaryLocationCalculations
 
-        private static void MergeHydraulicBoundaryLocations(IAssessmentSection targetAssessmentSection, IAssessmentSection sourceAssessmentSection)
+        private static IEnumerable<IObservable> MergeHydraulicBoundaryLocations(IAssessmentSection targetAssessmentSection, IAssessmentSection sourceAssessmentSection)
         {
-            MergeHydraulicBoundaryLocationCalculations(targetAssessmentSection.WaterLevelCalculationsForFactorizedSignalingNorm,
-                                                       sourceAssessmentSection.WaterLevelCalculationsForFactorizedSignalingNorm);
-            MergeHydraulicBoundaryLocationCalculations(targetAssessmentSection.WaterLevelCalculationsForSignalingNorm,
-                                                       sourceAssessmentSection.WaterLevelCalculationsForSignalingNorm);
-            MergeHydraulicBoundaryLocationCalculations(targetAssessmentSection.WaterLevelCalculationsForLowerLimitNorm,
-                                                       sourceAssessmentSection.WaterLevelCalculationsForLowerLimitNorm);
-            MergeHydraulicBoundaryLocationCalculations(targetAssessmentSection.WaterLevelCalculationsForFactorizedLowerLimitNorm,
-                                                       sourceAssessmentSection.WaterLevelCalculationsForFactorizedLowerLimitNorm);
+            var changedObjects = new List<IObservable>();
 
-            MergeHydraulicBoundaryLocationCalculations(targetAssessmentSection.WaveHeightCalculationsForFactorizedSignalingNorm,
-                                                       sourceAssessmentSection.WaveHeightCalculationsForFactorizedSignalingNorm);
-            MergeHydraulicBoundaryLocationCalculations(targetAssessmentSection.WaveHeightCalculationsForSignalingNorm,
-                                                       sourceAssessmentSection.WaveHeightCalculationsForSignalingNorm);
-            MergeHydraulicBoundaryLocationCalculations(targetAssessmentSection.WaveHeightCalculationsForLowerLimitNorm,
-                                                       sourceAssessmentSection.WaveHeightCalculationsForLowerLimitNorm);
-            MergeHydraulicBoundaryLocationCalculations(targetAssessmentSection.WaveHeightCalculationsForFactorizedLowerLimitNorm,
-                                                       sourceAssessmentSection.WaveHeightCalculationsForFactorizedLowerLimitNorm);
+            changedObjects.AddRange(MergeHydraulicBoundaryLocationCalculations(targetAssessmentSection.WaterLevelCalculationsForFactorizedSignalingNorm,
+                                                                               sourceAssessmentSection.WaterLevelCalculationsForFactorizedSignalingNorm));
+            changedObjects.AddRange(MergeHydraulicBoundaryLocationCalculations(targetAssessmentSection.WaterLevelCalculationsForSignalingNorm,
+                                                                               sourceAssessmentSection.WaterLevelCalculationsForSignalingNorm));
+            changedObjects.AddRange(MergeHydraulicBoundaryLocationCalculations(targetAssessmentSection.WaterLevelCalculationsForLowerLimitNorm,
+                                                                               sourceAssessmentSection.WaterLevelCalculationsForLowerLimitNorm));
+            changedObjects.AddRange(MergeHydraulicBoundaryLocationCalculations(targetAssessmentSection.WaterLevelCalculationsForFactorizedLowerLimitNorm,
+                                                                               sourceAssessmentSection.WaterLevelCalculationsForFactorizedLowerLimitNorm));
 
+            changedObjects.AddRange(MergeHydraulicBoundaryLocationCalculations(targetAssessmentSection.WaveHeightCalculationsForFactorizedSignalingNorm,
+                                                                               sourceAssessmentSection.WaveHeightCalculationsForFactorizedSignalingNorm));
+            changedObjects.AddRange(MergeHydraulicBoundaryLocationCalculations(targetAssessmentSection.WaveHeightCalculationsForSignalingNorm,
+                                                                               sourceAssessmentSection.WaveHeightCalculationsForSignalingNorm));
+            changedObjects.AddRange(MergeHydraulicBoundaryLocationCalculations(targetAssessmentSection.WaveHeightCalculationsForLowerLimitNorm,
+                                                                               sourceAssessmentSection.WaveHeightCalculationsForLowerLimitNorm));
+            changedObjects.AddRange(MergeHydraulicBoundaryLocationCalculations(targetAssessmentSection.WaveHeightCalculationsForFactorizedLowerLimitNorm,
+                                                                               sourceAssessmentSection.WaveHeightCalculationsForFactorizedLowerLimitNorm));
+
             log.Info(Resources.AssessmentSectionMergeHandler_MergeHydraulicBoundaryLocations_HydraulicBoundaryLocations_merged);
+
+            return changedObjects;
         }
 
-        private static void MergeHydraulicBoundaryLocationCalculations(IEnumerable<HydraulicBoundaryLocationCalculation> targetCalculations,
+        private static IEnumerable<IObservable> MergeHydraulicBoundaryLocationCalculations(IEnumerable<HydraulicBoundaryLocationCalculation> targetCalculations,
                                                                        IEnumerable<HydraulicBoundaryLocationCalculation> sourceCalculations)
         {
             for (var i = 0; i < targetCalculations.Count(); i++)
@@ -144,6 +156,7 @@
                 {
                     targetCalculation.InputParameters.ShouldIllustrationPointsBeCalculated = sourceCalculation.InputParameters.ShouldIllustrationPointsBeCalculated;
                     targetCalculation.Output = sourceCalculation.Output;
+                    yield return targetCalculation;
                 }
             }
         }
Index: Ringtoets/Integration/test/Ringtoets.Integration.Plugin.Test/Merge/AssessmentSectionMergeHandlerTest.cs
===================================================================
diff -u -rb2591925535d27b3d900f571bf7ffa80070b1aaa -r8536b5bd3d91298dc866db708d7c75ae10fc84de
--- Ringtoets/Integration/test/Ringtoets.Integration.Plugin.Test/Merge/AssessmentSectionMergeHandlerTest.cs	(.../AssessmentSectionMergeHandlerTest.cs)	(revision b2591925535d27b3d900f571bf7ffa80070b1aaa)
+++ Ringtoets/Integration/test/Ringtoets.Integration.Plugin.Test/Merge/AssessmentSectionMergeHandlerTest.cs	(.../AssessmentSectionMergeHandlerTest.cs)	(revision 8536b5bd3d91298dc866db708d7c75ae10fc84de)
@@ -654,6 +654,44 @@
             mocks.VerifyAll();
         }
 
+        [Test]
+        [TestCaseSource(nameof(GetCalculationsFuncs))]
+        public void PerformMerge_HydraulicBoundaryLocationCalculationsMerged_ObserversNotified(
+            Func<AssessmentSection, IEnumerable<HydraulicBoundaryLocationCalculation>> getCalculationsFunc)
+        {
+            // Setup
+            var mocks = new MockRepository();
+            var viewCommands = mocks.Stub<IViewCommands>();
+            var observer = mocks.StrictMock<IObserver>();
+            observer.Expect(o => o.UpdateObserver()).Repeat.Twice();
+            mocks.ReplayAll();
+
+            HydraulicBoundaryLocation[] locations =
+            {
+                new TestHydraulicBoundaryLocation(),
+                new TestHydraulicBoundaryLocation()
+            };
+
+            AssessmentSection targetAssessmentSection = CreateAssessmentSection(locations);
+            AssessmentSection sourceAssessmentSection = CreateAssessmentSection(locations);
+
+            IEnumerable<HydraulicBoundaryLocationCalculation> targetCalculations = getCalculationsFunc(targetAssessmentSection);
+            IEnumerable<HydraulicBoundaryLocationCalculation> sourceCalculations = getCalculationsFunc(sourceAssessmentSection);
+
+            targetCalculations.ForEachElementDo(calculation => calculation.Attach(observer));
+
+            SetOutput(targetCalculations);
+            SetOutput(sourceCalculations, true);
+
+            var handler = new AssessmentSectionMergeHandler(viewCommands);
+
+            // Call
+            handler.PerformMerge(targetAssessmentSection, sourceAssessmentSection, Enumerable.Empty<IFailureMechanism>());
+
+            // Assert
+            mocks.VerifyAll();
+        }
+
         private static void SetOutput(IEnumerable<HydraulicBoundaryLocationCalculation> calculations, bool illustrationPoints = false)
         {
             foreach (HydraulicBoundaryLocationCalculation calculation in calculations)