on my system it was exactly the same:
UUID has changed.
And i found out the reason:
First partition: Win-XP
Sec. partition: aptosid
third.partition: siduction
after my d-u in june or so ... the grub config has changed: because the 3.partition was suddenly the main system after d-u.:
"update-grub" only works from 3.part: siduction
...last year the main-system was the second-partition: update-grub works only from 2.part: aptosid
so i decided to manage "update-grub" from my admin-system: siduction (partition-3) only.
and: in june 2014 i found out: UUID has changed so i had to edit fstab in 3.partition and all was fine. (it was the time systemd journal found out that my system-time and bios-time was windows time
)