BuddyPress.org

if your server is running apache or litespeed, then you can just canonicalize or or use rewrite rules to redirect all traffic from blogname.www.domain.com to blogname.domain.com.

http://www.webweaver.nu/html-tips/web-redirection.shtml is one such tutorial using htaccess.

Or there might be something wrong with the code in buddypress.