As I started paying attention to the issue months ago, the only 'common' thread I could find is that the mob was moving to intercept me already. If I sent my pet to them, they would settle down into a fight zone, however, if the mob aggro'd on me and I sent Morris to intercept, the mob and Morris would see-saw toward me until they were in the dead zone then settle down. I think there's some kind of secondary aggro going on here...
I've sent Morris headlong into 2-4 mobs before, with a heal already on him and prior to their aggroing on him. As he draws all the mobs attention, I have my safety trap (usually freeze) set up and am standing on it (habit from PvP days, don't need to do this in PvE! Doh!). I crank off an aimed and then go into rotation. Strangely, 1 or 2 of the other mobs will then charge ME. How are they picking up this 'secondary' aggro on me when I'm casting against the main target whom Morris has totally entranced? They reach me, safety trap goes off and main target usually goes down about this time so Morris and I switch.
If this secondary aggro idea holds any water at all, it means that the target (and buddies) has to be aware that there's a hunter out there and the mob AI has been made smarter to go engage the hunter (no more free rides?).
This only seems to apply to social targets, and not groups of solo's. Maybe it's just the AI of the social Mobs that is a bit smarter?
Anyone else with observations along these lines?