The webmin dist of 1.020 is missing the 'config-gentoo-linux' file from the OpenSLP module.
Solution (not sure if this should go to Webmin bugtracker or here, please advise) cp /usr/libexec/webmin/openslp/config to /usr/libexec/webmin/openslp/config-gentoo-linux -Paul
fixed in portage. thanks :)