посмотрите на эту тему
http://bugs.typo3.org/view.php?id=11259
You are want to share cookies (sessions) between twitter.com and facebook.com. When accessing twitter.com, the browser will only send cookies created by twitter.com. When accessing facebook.com, the browser is not sending twitter.com cookies. You are trying and expecting that all of you browser cookies would be send to any domain, no matter which domain initially created them. This would be a major problem and would affect a user's privacy.
So there's no problem at all.