Specifically, I can lob a bunch of spells, and after a few dozen, when I cast with the right hand, or dual cast, I get a small blue flash, but no bolt of lightning. I've tested it on baddies, and it's not just the graphic effect that's gone, there's no damage done, yet it still drains magicka. It will still work for my left hand. And no, I'm not out of magicka, I can reproduce it with a full bar. It seems to be specific to the lightning family, because it also happens on chain lightning. And with chain lightning, mouse button 2 still works, as well.
It just started doing it recently (possibly right around 1.7, I don't use lightning bolts enough to be certain).
Is anyone else seeing this? Is there a fix, or even decent work around? I tend to just go to another spell until it works again, but I love lightning for fighting other spell slingers.