Comment 10 for bug 1315344

so, I just hit this issue using a custom install script running from a custom live CD, however I've managed to find where my issue was, just somehow happened to end up finding this page.

The issue was when I ran the grub install command, it would fail with the message that it can't find the md1 device.

I eventually noticed that for some strange reason, mdadm wasn't installed inside the chroot even though I'd told it too. Running apt-get install mdadm fixed the issue for me, so chances are mdadm isn't being installed into the chroot, so this is technically an issue with the ubiquity, I'd say, and not grub.