Fixed a bug where saves could be "lost" (the files would remain on disk as backup files, but the game would not "see" them) after quitting a game. This was due to the change number (CN) that Steam uses to decide whether to re-download files not incrementing properly in some cases.
This impacted Valve games, because of course it did. This fix also generally improves experience with first time sync of existing saves to a new Steam install. I don't know how I missed this issue until now, but it's fixed.