I have windows 7 64 bit; when I installed the .83 patch it blew away my mount point (mounted disk).
For whatever reason when I setup my system I had two disks; one became C and one was mounted under C (hind-site i would have just made it D). I installed my games on this second disk. WHen I installed the .983 patch; it blew way this mount point instead of installing the files in the game path.
Sadly I'm a linux person and not a windows person so I have no clue how this happened or what foobar this patch did to cause this mess.
Bit of a pain to get the disk remounted. Pretty please fix before the next patch; as it is now I have to revert to downloading the full game for updates until this is fixed....