Back in retail vanilla I remember going to SM as level 60, aggroing a lot of mobs and then aoe them down. This was possible because low level mobs would miss their attacks most of the time.
Tried it on other places, other lower levels mobs and the same thing happens: the melee mobs land ALL attacks like they have 100% chance to hit.
Is it a bug, or was it "fixed" in order to prevent gold farming? I hope it's a bug because so far most of the measures taken to prevent gold farming are taking away bits and pieces of vanilla as we knew it.