yeah I'm having this issue as well. I'm using the red prince and I can't use any other drudanae besides Griff's drudane.
My guess is it's and oversight and only that one item has the quest flag/property attached to it. The other thing could be that the quest it self is only set to recognize that one item. If I use that item to do Red's quest I have to kill Griff's gang or never turn the quest in if I don't want to lose those skill vendors. So I can't complete the quest to save Amryo or if I complete the quest to save amryo. I can't complete Red's personal quest.
