ubuntu 12.04 executing grub-install dummy failed

[John Center]

I installed the mdadm proposed update. I'm trying to install to an imsm raid1 array, using a btrfs filesystem on gpt partitions. My computer's BIOS can handle larger than 2TB drives, though it is not UEFI (Gigabyte x58a-ud3r rev 2 MB). I mounted the / partition afterwards & noticed that it installed to /, not @, though my user directory was installed to @home.

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: ubiquity 2.10.20
ProcVersionSignature: Ubuntu 3.2.0-29.46-generic 3.2.24
Uname: Linux 3.2.0-29-generic x86_64
ApportVersion: 2.0.1-0ubuntu12
Architecture: amd64
CasperVersion: 1.315
Date: Sun Sep 2 23:10:37 2012
InstallCmdLine: BOOT_IMAGE=/casper/vmlinuz file=/cdrom/preseed/ubuntu.seed boot=casper nodmraid quiet splash --
LiveMediaBuild: Ubuntu 12.04.1 LTS "Precise Pangolin" - Release amd64 (20120823.1)
ProcEnviron:
 TERM=unknown
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: grub-installer
UpgradeStatus: No upgrade log present (probably fresh install)