sessions in multiple browser windows

Hi all, I've got a session which is being maintained by cookies. One of the links on the page, when logged in, is a link the admin section of the site... at this stage, I have the link opening in a new window (target="_blank"). I've noticed that the session sometimes gets destroyed, with both windows losing session and forcing a new login. It's worth pointing out that losing the session doesn't always happen, or happen at a certain point, so I'm finding it hard to pinpoint the problem. Is this: a) the session now exists in two windows, and PHP doesn't like it, trashing them on purpose b) because I've got a problem with my session code somewhere ??? Many thanks, Justin French