function generate_board_url() on file /includes/functions.php line 1718 gets the name of the domain using the variable $_SERVER['SERVER_NAME'] .

I think this is wrong. It should be using $_SERVER['HTTP_HOST'] instead.

The reason is that HTTP_HOST can contain a subdomain whereas SERVER_NAME has only the TLD. So for example if you want your site to be called http://www.example.com, the way generate_board_url() works now will always return http://example.com .