Exactly - if you start on http, all the links are to the http version, and if you start on https all the links are https. Which has a more subtle but nasty security issue: even if you consistently view the forum over https, an active attacker that can modify your network requests can inject content into the next http page you view so that it causes a http request to the forum (for example an img tag referencing http://forum.bitcoin.org) and obtain your unencrypted cookie from that request. This is well within the capabilities of some Tor exit node owners.