CS:GO is an anomaly. I noticed it myself. I added CS:GO to my wishlist ages ago (when it was in beta) and then when it recently went on sale I noticed that the game's store page and list entry using Enhanced Steam was suggesting that it was not on my wishlist. It seems they changed entries or something at some point so the wishlisted version is not exactly the same as the version in the store. Just an oddity but like others said, usually steam will remove the entry from the wishlist if bought through steam. Redeeming codes is another matter though.