lol, it is having a negative impact on druids, rogues, healers in general, any comp with a mage, mages, BGs, PvE in general and even on game mechanics.
A resumed way to say it, is that when you spawn some NPCs or some NPCs alredy have some sub-npcs(such as Lord Rhyolith's boots), when they are killed/despawned/continues to exist, they do not automatically remove combat, they instead flag you as in combat with an unknown NPCs.
I can't report it yet since I need something more solid to make it easier to fix.