Force invalidate after load

Library/ContentProviders/MeshContentProvider.cs

@@ -102,6 +102,9 @@ namespace MatterHackers.MatterControl
 						sceneItem.Mesh = loadedItem.Mesh;
 						sceneItem.Children = loadedItem.Children;
 						sceneItem.Matrix *= Matrix4X4.CreateTranslation(-aabb.Center.x, -aabb.Center.y, -aabb.minXYZ.z);
+
+						// Notification should force invalidate and redraw
+						progressReporter(1, "");
 					}
 				})
 			};

PartPreviewWindow/View3D/DragDropLoadProgress.cs

@@ -86,12 +86,12 @@ namespace MatterHackers.MatterControl.PartPreviewWindow
 
 			if (progress0To1 == 1)
 			{
+				view3DWidget?.PartHasBeenChanged();
+
 				if (view3DWidget != null)
 				{
 					view3DWidget.AfterDraw -= View3DWidget_AfterDraw;
 				}
-
-				view3DWidget = null;
 			}
 		}
 	}