This has been an intermittent issue for me but if I use Fireball, enemies sometimes stop responding to any taunt from me but Fireball for the rest of a boss fight, which is obviously frustrating. No idea what's causing it or how to reproduce, it just randomly happens sometimes.
I had this happen to me the other day when I was tanking DM Elite with another tank and we were splitting up bosses. Fireball was the only power retaining aggro, and any other power would drop it.
That's a better way of wording it, actually. For me it was PCe. If I didn't reapply Fireball, non-tanks would pull aggro no matter how many other non-priority powers I was hitting the bosses with. It basically removed the ability for any/all other powers to taunt for me.
Here's an example of another issue with Fireball: Simply not working at all as a taunt against certain enemies. You can see it ignores Fireball completely but everything reacts to other taunts like usual.
