I'm unsure how this is possible, but the Ravenscar Hollow Cage Key seems to duplicate upon each visit to the dungeon if you don't take the key from the hagraven (0003D268). I found three copies of the key in its inventory, which is consistent with the number of times I had been to the dungeon; likely four because I already had one copy in my inventory.
Not sure which category this report should go under. Normally it would be actors, but it could be quests because it looks like the key may be handled by a quest alias related to the hagraven.