i found (through accieden) later that this is not a bug in sbackup but has to do with how nautilus (?) which is used to open the backup location shows the root directory initially:
it does show it as empty and only if one clicks in the file system navigation (top) bar on the icon to the left (a narrow rectangle) of the root (rounded square) icon. then root shows its content and one can select eg /media/disk/backup_folder_XX.
i found (through accieden) later that this is not a bug in sbackup but has to do with how nautilus (?) which is used to open the backup location shows the root directory initially: disk/backup_ folder_ XX.
it does show it as empty and only if one clicks in the file system navigation (top) bar on the icon to the left (a narrow rectangle) of the root (rounded square) icon. then root shows its content and one can select eg /media/