TKinter -- '<Destroy>' event executing more than once?

[Christopher Subich]

I'm building an application involving both twisted and Tkinter.  Since 
twisted co-opts <widget>.mainloop() in its reactor.run(), and since it 
behaves very badly if the application quits without reactor.stop() 
running, I attach the following function to '<Destroy>' in the main 
window (root = Tk()):

def stop_reactor_bind(x):
    reactor.stop()

Then:
root.bind('<Destroy>',stop_reactor_bind)

The problem, however, comes that when I add a Text widget inside the 
root window, upon destroying the window (closing it) the callback seems 
to execute twice.  In interactive testing, it's executed once per widget 
inside the root window.  Since twisted doesn't take multiple 
reactor.stop()s gracefully, how (short of wrapping this inside a 
class/scope that keeps state) can I ensure that the callback executes 
only once? Am I attaching to the wrong signal?