Following the RAID test case from the ISO tracker; installs fine, boots normally with both disks, boots fine with second disk disconnected, rebuilds array manually when second disk reconnected but grub won't boot with just the second disk in the array attached.
Reproduced on release images for Oneiric, amd64 and i386.
DistroRelease: Ubuntu 11.10
Package: grub2 (not installed)
ProcVersionSignature: Ubuntu 3.0.0-12.20-server 3.0.4
Uname: Linux 3.0.0-12-server x86_64
Date: Wed Oct 12 19:14:26 2011
InstallationMedia: Ubuntu-Server 11.10 "Oneiric Ocelot" - Release amd64 (20111011)
UpgradeStatus: No upgrade log present (probably fresh install)