PLEASE PAY ATTENTION:
I managed to trace this bug!!!
By printing array sizes, it turns out that it is the TEXT array that is the 
wrong size.
Force print statements of each array size.  You will find that on the 
initial creation, all sizes are correct.  After quitting and reloading, 
however, the text array is one character longer than it should be.

This is wreaking HAVOC with my attempts to deal with the final document 
character.

It looks like the BehaviorArray has an array that's one character smaller than
the text (although the problem could actually be somewhere else). Basically, try
starting Archy, LEAP to "O L D" to get near the end of the humane document, and
creep forward to the very last character. Once you get to the last character,
Archy will either crash with an out-of-bounds array index exception in the
behavior array, or (very weirdly) it will actually work but Archy will slow to a
crawl and eventually stop responding entirely.