I have a few random books and the amulet of talos that are quest items all of a sudden. I've sold like 3 amulets of talos why are they randomly becoming quest items? Does anyone else have this issue?

I'm having this problem as well. I also have some other items that I can't drop even tho their related quests are done. Im a bit sick of Bethesda not fixing this problem. Its not game breaking but its annoying.