I managed to upgrade by moving /etc/init.d/mdadm-raid and replacing with an empty script, upgrading and then moving it back.
-- Upgrading mdadm package is impossible - can't upgrade while raid arrays active https://launchpad.net/bugs/60623 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
