Some Quests only complete-able solo?

ereck1974

I was running the Spellplague quest with a cleric friend of mine, and we were doing fine right up to the end where you have to talk to Josef to end the quest. While both of us were in the party it simply would NOT let us finish the conversation with him and end the quest. We tried everything, talking to him while both were in range, having one of us get way out of range while the other talked to him, both of us trying to talk to him at the same time; nothing worked.

She quit out of the game, and went to bed, and as soon as she dropped from the party, I was able to talk to Josef and finish the quest.

I've seen this with a couple of other quests, but since I run a lot of them solo it may happen more often than I'm thinking.

WAI, known issue, or broken?