Non default BuddyPress themes don't use proper URLs on subdomains

(So far this has applied to the BlogsMU and Social themes - have yet to try the others)

We have BuddyPress installed on WP3.0 RC1 and on a subdomain only (i.e. restricted to just that site). The links on the default theme seem to work fine as they recognize the subdomain and use them, i.e., but on the other themes I use on BP, they revert to, not

How do I fix this?