grub installation during OS installation fails on software RAID using default partitioning

[Jason Harris]

While installing Ubuntu 14.04 LTS, installing to a software RAID array fails to install GRUB correctly.

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: ubiquity 2.18.7
ProcVersionSignature: Ubuntu 3.13.0-24.46-generic 3.13.9
Uname: Linux 3.13.0-24-generic x86_64
ApportVersion: 2.14.1-0ubuntu3
Architecture: amd64
CasperVersion: 1.340
Date: Mon Jul 28 20:26:38 2014
InstallCmdLine: BOOT_IMAGE=/casper/vmlinuz.efi file=/cdrom/preseed/ubuntu.seed cdrom-detect/try-usb=true persistent noprompt floppy.allowed_drive_mask=0 ignore_uuid boot=casper only-ubiquity quiet splash --
LiveMediaBuild: Ubuntu 14.04 LTS "Trusty Tahr" - Release amd64 (20140417)
ProcEnviron:
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: grub-installer
UpgradeStatus: No upgrade log present (probably fresh install)