I'm having a bit of issues with Devouring Plague, and wanted to know if others have the same problem.

Lets say i cast 2 x mind blast on a target dummy. The 3rd would make Devouring Plague castable, but if i cast mind blast on a raiders dummy, making it miss, the spell icon for Devouring Plague still happily starts glowing even though i only have 2 orbs. I've noticed this under other rare circumstances too.