Have had this issue on my magplar often and my keybind is tab (I like the pinky press, lol). I've got puncturing sweep on keybind 1 on one bar and purifying light on the other bar. I cannot even begin to describe how infuriated I get when I hear "whoosh, whoosh, whoosh" because I got stuck on bar and have now cast purifying light multiple times in a row. Even more infuriating when I need the fracking heal from sweep in something like vMA.