One character in the group got the cache key on completing the quest. The other got nothing on clicking the dialog. The quest remains in the quest log, but he asks why are you back?
This is the character I was using. The quest was again up. I ran it on both characters again, this time not in a group.
The quest bugged in exactly the same way on this character as it did before. I click the dialog, get no key. The dialog remains up, the world quest is still in the quest log.
When I leave the Broken shore and return, the quest does not reappear in the quest log.