Comment 4 for bug 225656

I'm very well aware on what fstab does, but that's not the issue here.
It's not about the partition being not accessible from within Ubuntu, but about being able to boot that partition.

The Hardy upgrade managed for some reason to make the windows partition marked as "hidden" and as a result, Windows XP could not be booted any more.

The user had to run some utility (partition magic, although (g)parted would have been another option) to recover this, unhide the partition, and be able to boot again into Windows.

Hiding a partition is all about setting the "hidden flag", see parted(8) fo rmore info.

The upgrade was performed with update-manager.