title: NULL tstate Error when using matplotlib together with Tkinter
body: <p>I draw some matplotlib.pyplot figures onto a Tkinter GUI. When I destroy the window the "Fatal Python Error" is raised. I seem to not be the only one with the problem but I cannot read a solution to it out of the discussions. 
  As it does not cause a real problem, but is just fairly inconvenient and has been bugging me for a while, I would be more than content with a way to just ignore and pass over it.</p>