"EFI install from DVD forgets previous EFI boot"
https://bugzilla.redhat.com/show_bug.cgi?id=809963#c7
"As far as sharing the same /boot/efi directory between installs, we don't
support that -- a new copy of the grub.efi binary is written as well as a new
grub.conf."
In a related case, anaconda states again that shared, merged grub.conf for EFI
booting is not supported:
"upgrade using boot.iso destroys EFI boot"
https://bugzilla.redhat.com/show_bug.cgi?id=816238
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