Game Mechanics: Mob HP's not moving while being killed - stuck at 100%

[Smoker]

I couldn't find this reported before.

While I have been grouped, mainly UGuk so far, I have noticed sometimes that the HP's of mobs will stay at 100% while being killed off by the other members of group. Even while mob is fleeing the HP's are at 100%, then it dies.

I haven't seen any repeatability to this.

Casting a dmg spell on the mob myself, does not help.
Retargeting does not help.
Other people see the mob's HP's falling.
Other people in the group sometimes have the same problem, but not two people at the same time.