Loathsome mire (bug?)

Just did a loathsome mire, got to the altar and when I clicked it, dropped an amulet and when I picked it up it immediately took the place of the one I had equipped and now I'm left with an amulet that does nothing for me. I feel like I've either missed something or this has got to be a bug. If I've messed up somehow I'll live with it but just feels odd.