[Grojlach]

Happened to me once as well; I lost my ring of free action for some strange reason and re-imported it into the game with Shadowkeeper; turned out that it wasn't really the ring of free action, but a cheat object with the same name, providing my character with 100 extra hitpoints and total immunity to all kinds of magic I think. So have you, by any chance, imported items with Shadowkeeper into the game?

EDIT: no wait, I've heard of this particular bug before I think, though it must've been at least a year ago that I last heard of it. It happened after character creation, right? Hmm, it happened that a Sorcerer with a certain Constitution got a totally wrong amount of hitpoints; have you installed the official patch? That should take care of that bug if it is really one.