i managed to build a live-build ISO.
Its /boot/grub/efi.img contains
which both show by "strings" the embedded configuration with
search --file --set=root /.disk/info
The ISO 9660 filesystem contains a file
So the riddle is why this does not get into effect with that particular
EFI implementation, and why a grub.cfg in the EFI System Partition
solves the problem.
Does a debian-cd ISO boot properly on that EFI ?
I meanwhile found out that the efi.img of debian-cd stems from
debian-cd_info.tar.gz created by
and that its grub-mkimage run needs no -c option because it has an -m option
with a grub.cfg file in the "memdisk" tarball. It's quite the same tarball
as created by live-build in
So it might be that debian-cd is affected as well.
If not, then differences between both ISOs might give hints about the cause.
Have a nice day :)