I have found that when doing the Decree quests in Vellosk and Neverdeath Graveyard, I get credit for Shadowvar Emissaries and Red Wizards of Thay killed by anyone just by being in the zones. I can just travel there and stay at the gate and complete the quests, as long as someone else is there actiely killing them. In the Chasm though, when going after the Plaguechanged Maws, I usually only get a kill if I'm the first to hit them (but not always). It really sux when I need 5 of them and there's a dozen of us on the quest.
Anyone else notice this? Is it a bug, or is it just me?