customer set ISO_DEFAULT="unattended" without anything changing. It seems that
there is an inconstancy in the evaluation of the value:

in doc/rear.8.adoc we have:
The +ISO_DEFAULT+ variable defines what default boot option is used on the
rescue image.-Possible values are `manual`, `boothd` or `unattended`.

in doc/user-guide/03-configuration.adoc:
_ISO_DEFAULT={manual,automatic,boothd}_

in usr/share/rear/lib/bootloader-functions.sh we check:    
 if [ "$ISO_DEFAULT" == "automatic" ]

in r/share/rear/restore/BAREOS/default/400_restore_backup.sh:
if [ "$ISO_DEFAULT" != "unattended" ]