I'm not yet sure why this happened, but to help you and everyone else out a little: If there's anything that changed, it's probably something pertaining to either UDisks or blkid. The former is the abstraction for mounting disk partitions etc. that Caja, Nemo and Disks all use; and the latter is used by UDisks to find the volume UUID or volume label.
Hopefully that might give you a head start in finding out what went wrong.