In /etc/security/concole.apps/isdn-config there is a line FALLBACK=true to enable a normal user to run the program even ehen authentication as root fails. But the program itself fails to run when not run as root. When a user starts isdn-config and he clicks on "run unprivileged" isdn-config complains about not being root and exits. So this parameter should be FALLBACK=false to hide that "run unprivileged" button.
It's fixed in isdn-config-0.17-9.