When setting the SelectedItem to null in the code behind the command is fired because internally in RadListBox we execute the command when the selection changes. As the ViewModel SelectedItem is bound to the RadListBox SelectedItem, setting the first to null causes a change in the selection.
Can you please provide more information, code samples or example to give more inside on the interesting behavior that occurs in your solution in order for me to assist you further.
Looking forward to your reply.
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