ChildNode(ShapeNode) on DiagramView cannot be removed when deleted with DeleteKey from ContainerNode.
Also, the exceptions below occur when the Node has selected and Drag&Dropped.

Message：
   Object reference not set to an instance of an object.
StackTrace：
   MindFusion.Diagramming.InteractionState.Start(PointF point, Diagram diagram)
   MindFusion.Diagramming.WinForms.Behaviors.BehaviorBase.OnMouseMove(Point mousePosition)
   MindFusion.Diagramming.WinForms.DiagramView.OnMouseMove(MouseEventArgs e)
   System.Windows.Forms.Control.WmMouseMove(Message& m)
   System.Windows.Forms.Control.WndProc(Message& m)
   MindFusion.Diagramming.WinForms.DiagramView.WndProc(Message& m)
   System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
   System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
   System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, WM msg, IntPtr wparam, IntPtr lparam)
   Interop.User32.DispatchMessageW(MSG& msg)
   System.Windows.Forms.Application.ComponentManager.Interop.Mso.IMsoComponentManag
er.FPushMessageLoop(UIntPtr dwComponentID, msoloop uReason, Void* pvLoopData)
   System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(msoloop reason, ApplicationContext context)
   System.Windows.Forms.Application.ThreadContext.RunMessageLoop(msoloop reason, ApplicationContext context)
   System.Windows.Forms.Application.Run(Form mainForm)

In the case of the above situation, what steps do I need to take?

Thank you for your response.

This was due to the fact that I had customized the ShapeNode and included a process to add it to Diagram in Constructor.
*The same node was being added to Diagram twice.

Regards,
Nobu