If you save your game while casting clairvoyance, and then reload that particular save, the blue smoke effect thingy will be floating in the air, even if you're not still casting the spell. The spell will just stay hanging in the air for all eternity (AFAIK). Shows up on both PS3 and Xbox.
there's no cure, but like I said it's harmless anyways. I had anther glitch to report, but I'm forgetting it now.