So I was fighting falmer in some dwarven ruin today, using my lightning bolt spell dual cast. Then I noticed it stopped working. I switched to firebolt, killed the falmer, then investigated this trying to fix it. Then I noticed no matter where I cast lightning bolt, my left hand spell would always hit this one spot on the floor. For anyone else having this problem, just leave the cell and it will be fixed. Can be annoying in a fight if you don't know what's going on, but it is still interesting.