Unfortunately, this is a known issue for us, and one we can't change anything at.
Keymailer is taking your owned games from your steam account. As soon as you owned game and gave it back or played a free weekend or pre-ordered, steam is storing data, and deletes almost everything, but keeps some left over data from the game (like a footprint). Keymailer is then detecting that data and shows the game as owned. Unfortunately, we can't access the steam data to delete the left-over, so we can't do anything :(
Have a nice day :)