Just to be clear, there are no GPT volumes and MBR volumes, only GPT and MBR disks if that is what you meant by volumes. To me, volumes means partitions.
Also if you use a MBR disk on a UEFI computer it can only boot if you change the UEFI setting to Legacy or CSM boot.
I can't answer the question on the Vista problem. From the FAQ it does say that Vista 64bit will boot on a GPT/UEFI disk. That would tell me something else is in play.
Can Windows 7, Windows Vista, and Windows Server 2008 read, write, and boot from GPT disks?
Yes, all versions can use GPT partitioned disks for data. Booting is only supported for 64-bit editions on UEFI-based systems.
You are correct, you can only boot a GPT disk on a UEFI computer. There a workarounds but it's not worth it.