That drives me crazy. Ok, it seems to be a minor problem, nothing gamebreaking (I hope), but I don't understand it at all. Especially after I did everything on a completely other pc, changed nothing and inserted only the two savegames.
I think I'll give up on it. Live is short after all, and I want to play this game so badly.
edit: Ok, the same issue reappeared - but with another spell - this time the telekinesis-spell. In the savegame I've uploaded (
http://www.mediafire.com/download/sgbebzddbix4eab/agssave.rar ) you stand at the tree in the north woods, were a bird's nest is. I've tried to "get" it down. The spell doesn't work (the game informs me, that I can't use the spell here) - and after that: The mousewheel doesn't respond (again, rightclicking works as usual, everything fine, but the mousewheel seems to be stuck). So the problem I have seems to have to do with trying spells on objects not intended for it. In the savegame, you still have to use the spell on the bird's nest.
edit 2: Ok, I have to correct me again: The problem appears everytime I use a spell on something not intended for it. I've tried to use the unlock spell on a tree (just to try), and the game says "You can't use the spell on that" - after that, mousewheel is broken. Same thing if I use the telekinesis-spell on something that isn't fetchable. So it seems to be in the gamefiles indeed. But if we both have the same version of the game I can't understand it.