I've noticed an issue with merc tanks and pulling with mez. If the player marked as puller in group breaks up a two pull by mezing one and Mez wears off before the one in camp is dead then sometimes the all the mercs will run to the mez mob no matter how far away it is.
I think I saw this last night in GMM a couple times. I was definitely set as the puller, I had definitely pulled by mezzing one and letting the other come to us. Later on in the fight, the tank merc took off, didn't see if the healer merc followed. In one case I may have pulled with tash and mezzed the mob outside the camp radius, but one of the times I definitely mezzed at the mob's spawn point.
Yes for me, at least in one of the cases. It just seemed like the merc ran really far, farther than they have for me in the past. I wasn't even going to post about it, but then I saw this thread and it matched my experience exactly.