Comment 1 for bug 236021

Based on a very quick code scan, I believe that this is an old bug never discovered rather than a recent regression (now that I think of it, I did see other people in the past unable to mount from vfat after kernel upgrade).

The initrd in the live cd explicitly adds vfat via casper hooks:

./hooks/casper:manual_add_modules vfat

but the same does not hold for regular initramfs-tools.

In particular, there is no vfat reference in initramfs-tools/hook-functions auto_add_modules>base and dep_add_modules. So when a new initramfs is generated there is no vfat.