The systemd service file for memcache, only starts memcache for /etc/memcache.conf. The old init script started one memcache instance for every /etc/memcache_$server.conf file. https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=784357 univention-saml and univention-self-service need the old behavior. For some reason invoke-rc.d calls the init script for memcache if called through another init script. But calls the service file if called directly on a console. Due to that univention-saml still works because it calls "invoke-rc.d memcached start" inside its own init script.
Should be fixed with Bug #45960. *** This bug has been marked as a duplicate of bug 45960 ***