Your PC's must be loading the main forum page from a cache. If there is an unread PM the server is going to send out that flashing banner at the top. If your PC has internet speedup software or some other form of caching then it may not actually load the page from the server. The PM popup is another thing - if you come to the site and click on a link before the page loads fully you won't see the popup. That popup uses Javascript and it's the very last thing on the page to load and it only shows you that popup on the very first page you come to the site on (that's why I added the flashing banner).