Pro Site - Domain Mapping and checkout page

With Pro Sites enabled and a sub blog with a mapped domain using the WPMU Domain Mapping plugin.

Lets assume:
Main site that offers Pro Site upgrade = http://topleveldomain.com
Mapped domain which is a sub blog on the main site = http://mappeddomain.com/

When you log in to the mapped domain and go to http://mappeddomain.com/wp-admin/, the link to the Pro Sites upgrade page links to http://mappeddomain.com/pro-sites/

NOT as one would expect it to go to: http://topleveldomain.com/pro-sites/

In this case - the upgrade page is unavailble.