on the way out from completing the "soul dust " quest I noticed "Shalak the Wise" had a lit question mark, on speaking to him I was given the "Golden Fang " quest which was a surprise as I'd already completed it. I also noticed that on completion of each of the component parts of the "soul dust" quest the success messages also repeated the messages from "soul dust" quest. think this should be corrected.
Most quests obtained in instances are repeatable and will reset if the instance does. The quest only grants half experience the second time you do it, and none on subsequent runs. Such quests are noted in your quest log by a small black and white circular icon.