Listbox dragRow

I think I may be having a senior moment! Since updating to 2019r1, my listbox dragging has gone a bit wonky. When I attempt to drag a row, it picks up and moves the window around instead! Check transparency of listbox - all OK - anyone else having this??? Ta in advance.

Found that self.NSWindowMBS.isMovableByWindowBackground = False in the windows open event fixes this.