This could be a problem with your initrd. Are you seeing /dev/mapper devices within your initramfs? Maybe initramfs-tools just forgot to include lvm support in your initrd?
-- root on lvm fails to boot. https://launchpad.net/bugs/29858 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
