It could have been caused by one of the rare books. There are a small assortment of books that, when read or used, will "swap" two attribute points. What you're describing here sounds like one of them (one I've actually seen before, too, but I can't remember the name of it). You may have found one of these books and then read it without paying much attention, which would trigger its effects. Since its an expendable item, the book would have then vanished, leaving no evidence other than the attribute changes. Unfortunately, short of reloading an earlier save from before it happened, there's not much you can do about it (at least until the Character Editors start rolling out).
