Setting session from within iframe?

I have a problem that maybe someone can shed some light on. I have a page, lets say it is located here... www.domain1.com On this page is a iframe with a src like so... www.domain2.com/mypage.php This php page has a session _start call in it. The problem is, the session cookie is not set when the php is called into an iframe. The session_id changes each time the iframe is refreshed. If I go to the page directly, then the cookie is set (and stays set). This happens in Safari, not FF. Is there some sort of bug that will not allow session cookies to be set when a page is called from an iframe? I have heard IE does this as well? -- Mike B^)>