Is this an old source silver mane? If so, that's the issue and you'll need to get a new source one (I think drop and re-do the quest? Not 100% sure on details)
assuming its the old source one (from the join date on forum it make sense) gotta drop the silver mane (don't drop the saddle), then get hog back, then get silver mane again (pretty sure you gotta get hog again at least). I had to drop my hog to get silver mane.
