Neat article, thanks!
A similar thing happened to me. I was making a little Pac-Man clone in flash for a class I was taking. Periodically a ghost would just bust through the wall and disappear. Sometimes it would come back through a different wall, but mostly it would just go off-screen never to be seen again (or until the next round). Turned out to be a rounding error that would let it bypass the wall detection and was a pain to debug. 
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Re: Going off the grid
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