I've had this bug since the launch of Murkmire. My assassin's scourge bow doesn't fire (and I do not mean that it has lag or latency). If I press the key assigned to the ability just once, the bow will most likely not fire. When this first happened, I would just try to hit it again on my next round of attacks. Nowadays I typically just spam the key several times until I've managed to get the bow to fire. Also, as far as I have seen, it's not a matter of lacking enough stamina to fire it.

It really screws up fights when you are waiting to see whether the damn bow will fire or not. Please, fix it.