Muti-Domain - New sites map to main site


I am having an issue with the multi-domain plugin.
I have followed the instructions but whenever a new user signs up to a domain (even the original domain) then the site created never has a sub-site prefix e.g. I create site but in my congratulations screen it tells me that the site created was
Has anyone else experienced this?
I am rolling back the plugin until I can get around this issue.

Many thanks,