Has any one ever got steam game revoked ?what game and why?

Does the warning popup always appear?
Because since I knew of this "issue" I started keeping a list of all the games in my library; today I was updating it and I found in there "Defense Grid 2" but there is no trace of such game in my current Steam library.
Also, I have marked the game as "free", in which I usually put those games whose keys are given for free from sites, devs etc.
It could also be a mistake of mine, not necessarily Valve's fault. Do any of you remember a Defense Grid 2 mass giveaway?

I got Skyrim revoked after I traded a guy my TF2 items for it. I think the reason was stolen credit card. I contacted steam support, told them about it, and they gave me the game.