Index: Ringtoets/Piping/src/Ringtoets.Piping.Service/PipingDataSynchronizationService.cs
===================================================================
diff -u -r1051f838aebbd5977351542027ce6330583b0d43 -rd9e5e7ea1e028347a738fc8e3d9c158a9b53ce15
--- Ringtoets/Piping/src/Ringtoets.Piping.Service/PipingDataSynchronizationService.cs	(.../PipingDataSynchronizationService.cs)	(revision 1051f838aebbd5977351542027ce6330583b0d43)
+++ Ringtoets/Piping/src/Ringtoets.Piping.Service/PipingDataSynchronizationService.cs	(.../PipingDataSynchronizationService.cs)	(revision d9e5e7ea1e028347a738fc8e3d9c158a9b53ce15)
@@ -20,6 +20,7 @@
 // All rights reserved.
 
 using System;
+using System.Collections.Generic;
 using System.Linq;
 using Core.Common.Utils.Extensions;
 using Ringtoets.HydraRing.Data;
@@ -36,12 +37,17 @@
         /// Clears the output for all calculations in the <see cref="PipingFailureMechanism"/>.
         /// </summary>
         /// <param name="failureMechanism">The <see cref="PipingFailureMechanism"/> which contains the calculations.</param>
-        public static void ClearAllCalculationOutput(PipingFailureMechanism failureMechanism)
+        /// <returns>An <see cref="IEnumerable{T}"/> of calculations which are affected by clearing the output.</returns>
+        public static IEnumerable<PipingCalculation> ClearAllCalculationOutput(PipingFailureMechanism failureMechanism)
         {
-            failureMechanism.Calculations
-                            .Cast<PipingCalculation>()
-                            .Where(c => c.HasOutput)
-                            .ForEachElementDo(ClearCalculationOutput);
+            var affectedItems = failureMechanism.Calculations
+                                                .Cast<PipingCalculation>()
+                                                .Where(c => c.HasOutput)
+                                                .ToArray();
+
+            affectedItems.ForEachElementDo(ClearCalculationOutput);
+
+            return affectedItems;
         }
 
         /// <summary>
@@ -63,12 +69,17 @@
         /// Clears the <see cref="HydraulicBoundaryLocation"/> for all the calculations in the <see cref="PipingFailureMechanism"/>.
         /// </summary>
         /// <param name="failureMechanism">The <see cref="PipingFailureMechanism"/> which contains the calculations.</param>
-        public static void ClearHydraulicBoundaryLocations(PipingFailureMechanism failureMechanism)
+        /// <returns>An <see cref="IEnumerable{T}"/> of calculations which are affected by clearing the output.</returns>
+        public static IEnumerable<PipingCalculation> ClearHydraulicBoundaryLocations(PipingFailureMechanism failureMechanism)
         {
-            failureMechanism.Calculations
-                            .Cast<PipingCalculation>()
-                            .Where(c => c.InputParameters.HydraulicBoundaryLocation != null)
-                            .ForEachElementDo(ClearHydraulicBoundaryLocation);
+            var affectedItems = failureMechanism.Calculations
+                                                .Cast<PipingCalculation>()
+                                                .Where(c => c.InputParameters.HydraulicBoundaryLocation != null)
+                                                .ToArray();
+            
+            affectedItems.ForEachElementDo(ClearHydraulicBoundaryLocation);
+
+            return affectedItems;
         }
 
         private static void ClearHydraulicBoundaryLocation(PipingCalculation calculation)