[Plugin: WordPress MU Domain Mapping] Cannot get "/" to be mapped get loop error

I ahev installed the plugin and the subsites map fine, but is there no way to map the “/” site? Is that just unusable when the plugin is installed? It only seems to work if WordPress is setup to have the root site by IP address not by any name. Is this by design or am I missing the way to hit the “/” site on an actual domain name?

http://ww.wp.xz.cn/extend/plugins/wordpress-mu-domain-mapping/