Package: os-prober Version: 1.51
Initially reported on https://bugs.launchpad.net/ubuntu/+source/os-prober/+bug/1038093
The os-prober of Ubuntu does not detect Fedora when Fedora's partition is unmounted (which is frequent). Consequence: Fedora does not appear in Ubuntu's GRUB menu.
WORKAROUND: mount the Fedora partition before doing update-grub in Ubuntu.
Bug confirmed by several French users with Fedora17 and Ubuntu12.04 (http://forum.ubuntu-fr.org/viewtopic.php?pid=9695571#p9695571 and http://forums.fedora-fr.org/viewtopic.php?id=57393 ).