Yeah, NS7 doesn’t really deal very well with that either. It kind of seems that the intention for both is that the server’s main FQDN be reserved for administration, and any web content would be via a virtual host with a different FQDN.
Edit: This suggests to me that the server’s “main” FQDN should be be one that’s reserved for administrative purposes, maybe even an “admin” subdomain or something similar.
Edit 2: This looks like a bug in the webserver module: it allows you to create a virtual host with the same FQDN as the main server FQDN–and once you do, you’re then locked out of the /cluster-admin/ system. This should probably be logged as a bug somewhere. @stephdl? @davidep? Any suggestions?