1.) It was only with duel-wielding from what I remember
2.) When I did it, the ability didn't even activate, as far as I know. Basically, I'd be clicking and using buttons, and it would try to use the ability, but I would use another ability, quickly, instead. Then, the button becomes greyed out like in the picture, so the cooldown never actually activated!
3.) It's happened once or twice with Hundred Fists, but also once with Slice