[2.50.1] [Win7] Selective Senility?

I can't easily detail how this happened, but I may as well report that it did:

While working on a quest, 2.50.1 decided that the key mapped to Button A (on keyboard mapping) no longer existed. It was absolutely convinced that pressing that key did nothing, but it did believe in the other keys. That's right, B, Start, R, and others worked, but A did not. I thought it could have had something to do with some scripts, but other quest files all did the same thing. Then, I exited 2.50.1, and reloaded it, and the problem was gone.

I have no idea how to replicate this, so I don;t know if reporting it has any value at all, but it was extremely strange. ZC had only been running for about three minutes too, so it wasn't one of those 'returning from sleep/loss of focus' problems. I know that @Saffith did things that change key-mapping behaviour with Allegro, so perhaps this is some very odd artefact of those.