Thanks: Frédéric Boiteux <fboiteux@calistel.com> for the bugreport
cat << EOF
menuentry "${title}" {
cat << EOF
menuentry "${title}" {
+$(prepare_grub_to_access_device ${GRUB_DEVICE_BOOT} | sed -e "s/^/ /")
iso_path="${rel_dirname}/$grml $CUSTOM_BOOTOPTIONS"
export iso_path
loopback loop "${rel_dirname}/$grml"
iso_path="${rel_dirname}/$grml $CUSTOM_BOOTOPTIONS"
export iso_path
loopback loop "${rel_dirname}/$grml"