I have like, no kidding 70+ duplicates of in my Unsorted wishlist. Deleting them by hand does nothing to remove them, and I can't delete the entire WL. It's maddening. It's basically a junk category I can't use functionally and it's been this way for at least a year+. I hope this gets fixed soon!
Out of curiosity, have you tried removing it from your wishlist by clicking the "- Wishlist" option on the item outside of the wishlist?