Alright. Do this. Turn into a troll. Go attack something. You can hit creatures that need magical weapons to hit, I'm assuming because of the DnD rule that lets creatures hit other creatures that need magic weapons to hit, based on the hit-dice of the attacking creature. Since you're a creature in troll form, I'm guessing this is why this works. If you're just in regular troll form, it works right forever.
Now, cast stoneskin. Then turn into a troll. The claws will work right. But, if the stoneskin wears off, or is chipped off, all of the sudden your claws will no longer work to hit creatures that require a magical weapon to hit. Same with ethereal visage, or a lot of other spells.
It's really annoying. I'm guessing this has something to do w/ swapping out of skins, and how spells work on skins. I don't really know.
I know I did find my human skin, w/ all it's stats and DP related +/- in my inventory a while later. Though, that's the first time I've ever had that happen.