Site keeps changing my mapped domain back to default

I'm trying to add a new site to my WPMU install that will have a unique domain name,

I have a dedicated IP address for this server. is pointed to this IP address.
My WPMU installation is the documentroot for that IP as set in the apache settings is set up and working.

When I try to go to it keeps changing things to the default domain

At first I thought this was because my .htaccess file had;

RewriteCond %{HTTP_HOST} !$ [NC]
RewriteRule ^(.*)$$1 [L,R=301]

But I commented that out and it's still changing the domain.

I did notice one thing that might explain this, when I am logged in the iknowjustice site and go to tools/domain mapping it gives me a space to type the domain in but when I do and click add it just returns me to the page with the blank domain and doesn't show that added domain anywhere. (see attached screenshot) Is that normal? or did something block it from being added.