The kernel (gentoo and vanilla) is using the wrong sector size for EFI GPT.
It uses strictly 512-byte sectors but it should be based on the logical block size.
Steps to Reproduce:
1. Make a GPT with a non 512 Sector size
2. Attach the drive to a gentoo based system
unknown partition table
use it as /dev/sdXY
You can get more information on this problem and a fix on linus' repo:
Can you/Have you applied those two patches referenced in your decription and determined if they fix the issue?
I added this to our SVN but I don't want to release a new kernel with it until I hear from your it works.
Released in gentoo-sources-2.6.32-r1