Can't delete actual inserted and selected nodes

I drag’n’drop a new node to my diagram. This node is selected and then I press the delete key. But the node wasn’t deleted.
I must select the node by clicking somewhere and select again to get it deleted by pressing the key.
It’s the same in the Flow Chart example.

How can I get the actual inserted and selected node to be deleted?

The problem is that the target diagram does not have focus, so the delete key is going to the source diagram.

Implement an ExternalObjectsDropped event handler that changes focus to the diagram.

Thank you for the answer.
I can’t get the ExternalObjectsDropped Event handler to fire his event, so I set the Focus at the end of my Drop event handler - this works.