Best way to explain this is an example:
If I have fire-arrow active but I decide actually, I'd rather use poison arrow, if I click poison-arrow on my action bar, it will shoot the fire-arrow in the direction of the mouse on the action bar.
This seems like a bug - clicking on the action bar should cancel the currently selected ability not active/fire it. I'm aware you can press escape to cancel it but its easy to forget since its not intuitive in a game to do so.
