Hi, I'm not sure if this is a bug or not. We encountered this yesterday when playing. Sebille (whom we had made into a wizard this time around) ate that head that adds First Aid skill, we were very happy that she got it, seemed very handy. It was right there in the action bar, memorized, all was well.
THEN we also got some cool trousers for her, mage trousers I think, instead of some lousy +2 to PA fashion disaster. BUT the moment we equipped the mage pants, a notice appeared that a skill has been removed from memorized because the prerequisites were no longer met. We checked and sure enough, First Aid was still among the skills she had, but we couldn't drag it right to be memorized, it always said that since she doesn't have Huntsman 1, she can't have it.
It shouldn't be like this, right?
(Not trying to whine, though, the game is awesome, guys!)