Flame Breath not spending rage

I am having a bug where flame breath does not spend rage at all, and only ever lasts the initial 4 seconds. It's worked that way since I unlocked it. I don't have another character high enough level to test if this is a bug specific to this one toon, or universal for me.

are you using mouse movement? if so it doesn't work because as soon as you try and move it cancels the channel.