Comment 1 for bug 780198

Perhaps the following link will help clarify this issue:

http://ubuntuforums.org/archive/index.php/t-1722471.html

Recently, I suffered with the same problem installing 10.4 on two 2Tb drives in RAID 1 configuration. Following the guidelines outlined in the link above everything installed fine.

The highlights are:

1. Create a 1Mb BIOS boot partition one both drives (assuming RAID 1) but don't create RAID device on these partitions
2. Don't use/need a /boot partition
3. Don't worry about setting any partition to bootable
4. Create the rest of the partitioning scheme as always setting the physical device partitions to RAID.

There may still be a bug but in my case following these guidelines got my system up and running with no problems.

Hope this helps.