Memory exception with Tkinter root.quit

[Jane Austine]

>>> from Tkinter import *
>>> r=Tk()
>>> b=Button(r,text='Quit',command=r.quit)
>>> b.pack()
>>> r.mainloop()

And when I press the "Quit" button the mainloop exits. After that, if
I finish the python shell, a memory exception occurs.

This is Windows XP machine with Python 2.3.

Can anyone see the problem?

Jane