Maybe you could put a hard limit to the size? Like, if the player's size x is 9+e99 the text still tells them they gained some size but the game doesn't register the increase
Yeah, that's what I did, at least I thought. Somehow that still went wrong.
Actually, now that I think of it I'm pretty sure I know why. I limited the size stat after applying special effects from spells/potions/etc, so then maybe the problem is caused by your base size before special effects being too big