how to reproduce:
click on a npc to start dialog
click the node that ends the dialog, and click a few times directly afterwards
=> the dialog will reopen, altough the cursor does NOT hover the npc anymore.
Right after closing the dialog window, the npc is still highlighted (altough not
covered by cursor), so when you click again, the dialog is started again.
As soon as the npc moves a bit or the mouse is moved a bit, the highlight is gone.
I guess we can fix this by adding some kind of mouse-cursor-position-update
trigger after closing any kind of window.