Comment 2 for bug 1017678

With the update to 3.5.0-2-generic in quantal, /boot/grub/grub.cfg was generated. When running update-grub from the precise partition, the grub2 menu is now correct without duplicates (plus additional recovery mode entries).

So I guess this is only an issue after an initial install using: ubiquity -b; to skip installing the boot loader. Once grub.cfg is generated, os-prober doesn't have to guess with 90fallback and we don't get duplicates.