grub-pc fails to upgrade with raid disks

When performing a regular upgrade an upgrade to grub-pc was scheduled. When this got to configuring it reported "grub-install: error: disk `md0' not found." for all 4 /dev/sdX devices in the system. The 4 drives have a RAID1 array for /boot and a RAID5 LVM device for the rest of the storage, so grub needs to be installed in the boot sector for all four drives.

Running grub-install manually for the drives resutls in -

# grub-install /dev/sda
Installing for i386-pc platform.
grub-install: error: disk `md0' not found.

So, this doesn't fill me with confidence that the server is going to reboot nicely without intervention from a rescue disk.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: grub-pc 2.02~beta2-36ubuntu3.18
ProcVersionSignature: Ubuntu 4.4.0-116.140-generic 4.4.98
Uname: Linux 4.4.0-116-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.15
Architecture: amd64
Date: Thu Mar 29 16:06:26 2018
InstallationDate: Installed on 2012-03-20 (2199 days ago)
InstallationMedia: Ubuntu-Server 11.10 "Oneiric Ocelot" - Release amd64 (20111011)
ProcEnviron:
 TERM=screen
 SHELL=/bin/bash
 PATH=(custom, user)
 LANG=en_GB.UTF-8
 LANGUAGE=en_GB:en
SourcePackage: grub2
UpgradeStatus: Upgraded to xenial on 2016-08-08 (597 days ago)