hey, people!
I have the same problem with 6.2 on a virtualbox.
6.1 works on both disks, but 6.2(last kernel) only on sdb.

It's strange, but i think, i solved this problem...
i loaded with 6.1 on sda, and then:

just change in /etc/grub.conf, in that part, where newer kernel is written about :

root=uuid=blabla656585

to

root=/dev/md0

and it works. no kernel panic, no other xxxx [Moderator edit] stuff.

and it have another string, about 6.1 with root=uuid=...blbla, and it works too
strings looking the same at their another parts

I really don't understand, why it works. but - it works. may be this helps to find a bug.

sorry about bad english.
i will be glad, if somone will teach me, why it works.)