At the moment I’m playing Dragon Age Origins - it was included in one of the Humble Bundles. The game has been installed through Steam and everything was fine. Until I started Origin. Dragon Age was also in my Origin Library, and Origin started downloading a patch. I wondered why Steam hasn’t found an update and went on.
After a while I tried to start Dragon Age via Steam. Doesn’t work anymore, it aborts with a strange error message. Starting the game with Origin works fine.
WTF? Thanks Origin! Now I have Dragon Age in my Steam library but can’t start it. Nice.