There are a number of quests in TOA that are flagged as "battlegroup friendly." That means that everyone in a battlegroup that is on a particular step in a quest can all get bumped to the next step together.
Not ALL TOA quests are so flagged, however! For example, the duel with Krojer isn't meant to be done with a group at all, so only one person will get the quest credit. And some quests can clearly be done with only one group, so even if a battlegroup does it, only one group will get the quest credit.
(Battlegroup questing is only enabled in TOA at this time - no classic or Shrouded Isles quests are currently flagged.)
So it's not a bug if your whole battlegroup doesn't get quest credit on an easier, one group encounter. Not every quest is flagged to give credit to a battlegroup.