When you're in a team and you aren't the team leader you can't talk to npcs to get the quests, and if the team leader accepts the quest, the quest will not appear as taken to the other members of the team!
well I think it's  a bug!

Only the team leader could talk with the NPC and carry on some actions.
If you need to talk with the NPC while you are in a team, you have to leave the team first.

ow, I thought it was a bug!