Installer should ensure a Boot BIOS partition is created on GPT when BIOS is non-EFI
I did a fresh install of 12.10 on a new SSD and used the installer to partition the drive. I had chosen 'Something Else' for installation type (http://
The installer should try to detect this situation and prevent it. When I ran Boot Repair it was able to tell me I had a GPT drive on a non-EFI BIOS with no Boot BIOS partition, so it is possible.