Tkinter Caesar Cipher GUI (speed errors?)

[Andrew Free]

I have been told the mailing lists talk a lot about Tkinter and I have  
not been able to find anyone who knows the answer to this question.  
This is also the first time I have used the mailing lists, so hey  
guys :D.

I decided to work on a GUI for this because I need the practice.  
However I ran into this weird problem.
If I change line 67 from 1000 to 100 my program prints two of the last  
letter...http://pastebin.com/d656cfd09
(with 1000) http://www.grabup.com/uploads/9d477c68231951f4025a27090de798e1.png?direct
with (100) http://www.grabup.com/uploads/8adfdc83e9b5a2e9e7af1f557a97a3ee.png?direct

That just makes no sense at all. Is 100 to fast for it to run? I would  
think it would wait for it to finish and update the GUI before it  
moved on.

Thanks,

Andrew
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