I've seen that bug before 1.5, my alt didn't get credit for killing the harvester boss in there at first try while doing the dungeon quest, and now I saw it again with the pledge. We killed the harvester but the quest pointer stayed there, telling us to kill her again. We restarted the dungeon and it worked that time, guess should be thankful for that. Also for the fact that it wasn't last boss - would be REALLY sad to go all the dungeon(as amazingly beautiful as it is) only to have it bug out in the very end. >.>