The EFI stores the GUID (Global Unique Identifier) of each boot option. It is a 128bit (I think!) binary number that uniquely identifies the boot partition. The same number is stored inside the boot block on the system disk.

When the EFI attempts to boot using a boot option a check is made to compare the GUID stored in the console to the one stored on the disk. If there is no match, the boot option will not work.

When restoring a BACKUP/IMAGE, the backup utility calls $SETBOOT to create the boot block on your new system disk. $SETBOOT generates a new GUID so the one stored in the console does not match the one stored in the EFI and you have to re-validate the boot option.

While working in HP, I have modified BACKUP to preserve the GUID inside the save-set header, what is currently missing is a mechanism for BACKUP to pass the GUID to $SETBOOT and instruct $SETBOOT to avoid creating a new GUID.

$ boot :== $sys$system:sys$setboot.exe                                  
check GPT.SYS mit
$ boot -s -f SAN-SYSTEMDISK: