Public bug reported:

Binary package hint: util-linux

Ubuntu 7.10, util-linux 2.13-8ubuntu1.

If the only change to a disc's MBR in fdisk is to use the `expert'
menu's `i' option to set the MBR's Window NT's ID, now used by Linux for
EDD, then the altered partition isn't written back to disc so the change
isn't done.  This seems to be because write_table() doesn't call
write_sector() which calls write(2) unless one of the four primary
partition entries has been altered, which is the case of `i', they
haven't.

fdisk misleadingly goes onto say

    Expert command (m for help): w
    The partition table has been altered!

    Calling ioctl() to re-read partition table.

    WARNING: Re-reading the partition table failed with error 16: Device or 
resource busy.
    The kernel still uses the old table.
    The new table will be used at the next reboot.
    Syncing disks.

but this isn't true and on the next reboot the old ID will still be
present.  This can also be seen with a hexdump before reboot, "hexdump
-C -s 440 -n 4 /dev/sda".

** Affects: util-linux (Ubuntu)
     Importance: Undecided
         Status: New

-- 
fdisk doesn't write MBR if only Windows NT ID is changed.
https://bugs.launchpad.net/bugs/225564
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