That is strange, and I'm pretty sure the Steam version comes fully patched. Try this; backup your saves, then use the Steam menu to 'refresh cache/game files' and 'check for updates'. I've never heard of a faulty installation using Steam, but I guess it's possible. Since you've made zero changes to the game, this is likely something you'll have to contact Steam support about. Just make sure you keep a separate copy of your save folder.