This is strictly an image build issue; livecd-rootfs diverts all of grub-probe in the divert_grub() function, but it really should only do this for 30_os-prober.
We already run update-grub correctly; the issue is that some of these calls may happen with grub-probe diverted in such a way that the grub.cfg will get mangled a bit, dropping the right path for the search command used to find the root.
This is strictly an image build issue; livecd-rootfs diverts all of grub-probe in the divert_grub() function, but it really should only do this for 30_os-prober.
We already run update-grub correctly; the issue is that some of these calls may happen with grub-probe diverted in such a way that the grub.cfg will get mangled a bit, dropping the right path for the search command used to find the root.