diff --git a/MatterControlLib/DesignTools/Operations/AlignObject3D.cs b/MatterControlLib/DesignTools/Operations/AlignObject3D.cs
index 6d322c381..121107dc1 100644
--- a/MatterControlLib/DesignTools/Operations/AlignObject3D.cs
+++ b/MatterControlLib/DesignTools/Operations/AlignObject3D.cs
@@ -234,7 +234,7 @@ namespace MatterHackers.MatterControl.DesignTools.Operations
 			{
 				if (SelectedChild.Count > 0)
 				{
-					return this.Children.Where(c => c.ID == SelectedChild[0]).FirstOrDefault();
+					return this.Children.Where(c => c.ID == SelectedChild.First()).FirstOrDefault();
 				}
 
 				return this.Children.FirstOrDefault();
diff --git a/MatterControlLib/DesignTools/Operations/Object3DExtensions.cs b/MatterControlLib/DesignTools/Operations/Object3DExtensions.cs
index 7de7029d3..de5b65d0a 100644
--- a/MatterControlLib/DesignTools/Operations/Object3DExtensions.cs
+++ b/MatterControlLib/DesignTools/Operations/Object3DExtensions.cs
@@ -270,7 +270,7 @@ namespace MatterHackers.MatterControl.DesignTools.Operations
 			subtract.Children.Add(a.Clone());
 			var bClone = b.Clone();
 			subtract.Children.Add(bClone);
-			subtract.ItemsToSubtract.Add(bClone.ID);
+			subtract.SelectedChildren.Add(bClone.ID);
 
 			subtract.Subtract();
 
diff --git a/MatterControlLib/PartPreviewWindow/View3D/Actions/SubtractAndReplaceObject3D_2.cs b/MatterControlLib/PartPreviewWindow/View3D/Actions/SubtractAndReplaceObject3D_2.cs
index f9d263402..41a6c1560 100644
--- a/MatterControlLib/PartPreviewWindow/View3D/Actions/SubtractAndReplaceObject3D_2.cs
+++ b/MatterControlLib/PartPreviewWindow/View3D/Actions/SubtractAndReplaceObject3D_2.cs
@@ -176,7 +176,12 @@ namespace MatterHackers.MatterControl.PartPreviewWindow.View3D
 				{
 					SubtractAndReplace(cancellationToken, reporter);
 					var newComputedChildren = new SelectedChildren();
-					newComputedChildren.AddRange(SelectedChildren);
+
+					foreach (var id in SelectedChildren)
+					{
+						newComputedChildren.Add(id);
+					}
+
 					ComputedChildren = newComputedChildren;
 				}
 				catch
diff --git a/MatterControlLib/PartPreviewWindow/View3D/Actions/SubtractObject3D.cs b/MatterControlLib/PartPreviewWindow/View3D/Actions/SubtractObject3D.cs
index 7999bd9b9..dfebce19a 100644
--- a/MatterControlLib/PartPreviewWindow/View3D/Actions/SubtractObject3D.cs
+++ b/MatterControlLib/PartPreviewWindow/View3D/Actions/SubtractObject3D.cs
@@ -53,9 +53,7 @@ namespace MatterHackers.MatterControl.PartPreviewWindow.View3D
 			Name = "Subtract";
 		}
 
-		public SelectedChildren ItemsToSubtract { get; set; } = new SelectedChildren();
-
-		public SelectedChildren SelectedChildren => ItemsToSubtract;
+		public SelectedChildren SelectedChildren { get; set; } = new SelectedChildren();
 
 		public override async void OnInvalidate(InvalidateArgs invalidateType)
 		{
@@ -115,13 +113,13 @@ namespace MatterHackers.MatterControl.PartPreviewWindow.View3D
 
 			bool ItemInSubtractList(IObject3D item)
 			{
-				if (ItemsToSubtract.Contains(item.ID))
+				if (SelectedChildren.Contains(item.ID))
 				{
 					return true;
 				}
 
 				// check if the wrapped item is in the subtract list
-				if (item.Children.Count > 0 && ItemsToSubtract.Contains(item.Children.First().ID))
+				if (item.Children.Count > 0 && SelectedChildren.Contains(item.Children.First().ID))
 				{
 					return true;
 				}
diff --git a/MatterControlLib/PartPreviewWindow/View3D/Actions/SubtractObject3D_2.cs b/MatterControlLib/PartPreviewWindow/View3D/Actions/SubtractObject3D_2.cs
index 3f427c478..ca2842cf5 100644
--- a/MatterControlLib/PartPreviewWindow/View3D/Actions/SubtractObject3D_2.cs
+++ b/MatterControlLib/PartPreviewWindow/View3D/Actions/SubtractObject3D_2.cs
@@ -63,8 +63,7 @@ namespace MatterHackers.MatterControl.PartPreviewWindow.View3D
 				var parentOfSubtractTargets = this.SourceContainer.DescendantsAndSelfMultipleChildrenFirstOrSelf();
 
 				var removeObjects = parentOfSubtractTargets.Children
-					.Where((i) => SelectedChildren
-					.Contains(i.ID))
+					.Where(i => SelectedChildren.Contains(i.ID))
 					.SelectMany(c => c.VisibleMeshes())
 					.ToList();
 
@@ -74,8 +73,7 @@ namespace MatterHackers.MatterControl.PartPreviewWindow.View3D
 				}
 
 				var keepItems = parentOfSubtractTargets.Children
-					.Where((i) => !SelectedChildren
-					.Contains(i.ID))
+					.Where(i => !SelectedChildren.Contains(i.ID))
 					.ToList();
 
 				foreach (var keepItem in keepItems)
diff --git a/MatterControlLib/SlicerConfiguration/UIFields/ChildrenSelectorListField.cs b/MatterControlLib/SlicerConfiguration/UIFields/ChildrenSelectorListField.cs
index cdb524efa..bc264ba6a 100644
--- a/MatterControlLib/SlicerConfiguration/UIFields/ChildrenSelectorListField.cs
+++ b/MatterControlLib/SlicerConfiguration/UIFields/ChildrenSelectorListField.cs
@@ -60,7 +60,7 @@ namespace MatterHackers.MatterControl.SlicerConfiguration
 				names = item.Children.Select(child => (child.ID, child.Name)).ToList();
 				if (item.SelectedChild.Count == 1)
 				{
-					selectedID = item.SelectedChild[0];
+					selectedID = item.SelectedChild.First();
 				}
 			}
 
diff --git a/Submodules/agg-sharp b/Submodules/agg-sharp
index ad8d39a9d..f8d12266e 160000
--- a/Submodules/agg-sharp
+++ b/Submodules/agg-sharp
@@ -1 +1 @@
-Subproject commit ad8d39a9d72bbf560a4b235a7979411b79327c2d
+Subproject commit f8d12266e143e85835e5940166fb7d13c67791b6
diff --git a/Tests/MatterControl.Tests/MatterControl/InteractiveSceneTests.cs b/Tests/MatterControl.Tests/MatterControl/InteractiveSceneTests.cs
index 9e1c7f6e8..7e4269688 100644
--- a/Tests/MatterControl.Tests/MatterControl/InteractiveSceneTests.cs
+++ b/Tests/MatterControl.Tests/MatterControl/InteractiveSceneTests.cs
@@ -276,7 +276,7 @@ namespace MatterControl.Tests.MatterControl
 				var subtract = new SubtractObject3D();
 				subtract.Children.Add(cubeA);
 				subtract.Children.Add(offsetCubeB);
-				subtract.ItemsToSubtract.Add(offsetCubeB.ID);
+				subtract.SelectedChildren.Add(offsetCubeB.ID);
 				root.Children.Add(subtract);
 
 				subtract.Subtract();