Hypersmurf
Moderatarrrrh...
Oh crap...
I don't usually put it quite so strongly, but the sentiment is right

For the record, I agree with Judas... and I'll go further and say that the Defender no longer benefits from the increased hardness, hit points, and immunity to weapons with a lesser enhancement bonus it would normally have for being a +1 sword.
Thus, if your sword has been bashed about a bit, it's entirely possible for it to snap when you reassign your plusses.
-Hyp.