Alright so this has been happening pretty frequently, although there doesn't seem to be any rhyme or reason to it.
I could be doing just about anything and the game just locks up. When I close it I notice...every time...that Steam updates the game. It isn't much, takes about two minutes. One time I had an error message about my save files not being synced properly with Steam's; I feel that's somehow related.
Sometimes even if it doesn't completely crash, certain corruptions begin to occur, like the outyline around a selected army disappearing, the outline of a city's ZOC disappearing, or other buggy behavior with units (creating doubles of themselves and not moving properly, for example). In these cases, if I close the game, again I notice Steam has to update something. This has probably happened 15-20 times in the last week.
What gives? Is there anything I can do to keep this from happening?