They are returning back!
The healers that haven't nothing other to do than put a regen on you the instant before you are taking aggro from a group of mobs.
Dudes, I don't want play an aggro war with you, why are you testing me at every pull? Why I have to watch out even for my healer other than the bad guys?
What worsen the situation, the couple mobs that maybe have to retake aggro are running away the pack because healer running around the map as an headless chicken, instead of taking mobs to me. I'd start to think he wanted a scene of merry-go-round to screenshot...