It's clearly a bug, just like in top there was auto attack bug that was 1 shoting tanks at the moment when it shouldnt happen. Just because its not even remotely as bad as there, it dont mean it shouldnt be fixed. On the other hand if that was designed this way instead of just increasing dmg a lil bit, then it was lazy design. First damage from thin air, next thing will be mechanics without any indicators like in wow, if we allow devs to do it this way.