Some additional info -
I can add my backup Win8 install on D1, P1 to the UEFI boot menu (on D0) with EasyBCD. Note that D1 is a MBR-formatted disk. When I am in the UEFI boot menu (on D0), I can select either my Win7 install (on D0, P3) or my Win 8 install (on D0, P4), and both boot fine...