I don't know if this works for the Mac version or not, but it's worth a shot. I noticed that whenever the game loads a new mod, it tends to break. That is if I switch from Main to Purchasable skillbooks, or another mod for that matter, when I start a new game or try to load the mod into another save, the skills are usually messed up and will either cause the game to crash when trying to use them or simply do nothing at all or as Skyria mentioned above, use an entirely different skill. My solution on the PC is to actually activate the mod in game, then quit out of the game and reload the game with that mod activated at the start. This forces the game to reload the entire package which it doesn't seem to do correctly when you simply switch in game. Dunno if that will fix your problem Skyria, but it seemed to work 100% of the time for me on the PC version so it's probably worth a shot at least.
