Deleted Questions in Favorites
Minor issue. If you try to favourite a deleted question (hey, I was curious), the star lights up and the count increments, but there's no popup error like you get if you try to vote: "This post has been deleted; deleted posts can't be voted on. (click on this box to dismiss)"
The vote doesn't actually go through, but the counter and star status isn't reset until the page is reloaded.