Comment # 19 on bug 1220276 from Michael Chang

I believe the issue Lukas encountered could be avoided if the system always
reused an existing EFI system partition, even when installing on separate
disks. However, I still prefer not to reuse an ESP that isn't on one of the
target disks where the new system will be installed. This makes the setup
easier to maintain since the boot disk is directly associated with the system,
allowing for easier movement between systems.

I also think Lukas's problem was partly due to odd firmware behavior. During
grub2-install or shim-install, a new boot entry is registered to point to the
new ESP and its bootloader. Additionally, this process reorders the BootOrder
to prioritize the new entry, making the system boot the latest installation
upon the next reboot.

However, something disrupted the BootOrder, and I suspect it was the Fast Boot
feature in UEFI. Fast Boot only initializes the subsystems needed for the top
boot disk in the order. It seems the new boot entry was ignored because the
boot disk order settings overrule the BootOrder settings.