working on combine test fail

fix flatten

MatterControlLib/DesignTools/Operations/OperationSourceObject3D.cs

@@ -29,7 +29,6 @@ either expressed or implied, of the FreeBSD Project.
 
 using System.Collections.Generic;
 using System.Linq;
-using System.Threading.Tasks;
 using MatterHackers.Agg.UI;
 using MatterHackers.DataConverters3D;
 using MatterHackers.DataConverters3D.UndoCommands;
@@ -41,6 +40,8 @@ namespace MatterHackers.MatterControl.DesignTools.Operations
 {
 	public class OperationSourceContainerObject3D : Object3D
 	{
+		public override bool CanFlatten => true;
+
 		[JsonIgnore]
 		public IObject3D SourceContainer
 		{

Tests/MatterControl.Tests/MatterControl/InteractiveSceneTests.cs

@@ -72,6 +72,14 @@ namespace MatterControl.Tests.MatterControl
 				union.Children.Add(offsetCubeB);
 				root.Children.Add(union);
 
+				Assert.IsTrue(union.GetAxisAlignedBoundingBox().Equals(new AxisAlignedBoundingBox(
+					-10, -10, -10,
+					20, 10, 10), .001));
+
+				Assert.IsTrue(root.GetAxisAlignedBoundingBox().Equals(new AxisAlignedBoundingBox(
+					-10, -10, -10,
+					20, 10, 10), .001));
+
 				union.Combine();
 				Assert.IsTrue(union.GetAxisAlignedBoundingBox().Equals(new AxisAlignedBoundingBox(
 					-10, -10, -10,