This is caused by MultiCall's _ComplexBinder.__del__() being called during app shutdown. _ComplexBinder.__del__() unbinds a bunch of event handlers from the widget to which it is attached. It seems that there's some edge case here where the underlying Tk widget has already been destroyed.

Instead of trying to debug all of the Tk events and app shutdown order, I propose just surrounding this __del__() code with a try/except block, catching _tkinter.TclError and ignoring it. From my (somehwat limited) understanding of MultiCall, this shouldn't do any harm.

See attached patch.