It turns out that mdadm had been uninstalled some two weeks prior to the most recent upgrade and so grub-install had no user space tools to query the RAID arrays. Reinstating mdadm fixed the problem.
It turns out that mdadm had been uninstalled some two weeks prior to the most recent upgrade and so grub-install had no user space tools to query the RAID arrays. Reinstating mdadm fixed the problem.