I think you've figured it out. If you leave your browser open to a forum page, the site believes you are still connected and not in need of updates. (Actually, it's a bit more complicated than that, but the end result is the same.) I say "I think" because I'm not really sure, but it's a plausible explanation. In theory, you would have to be doing something, like hitting update now and then, for this to happen, but if you're on the home page, the chatbox is effectively doing that for you. There may be other pages where the browser periodically pings the server behind the scenes keeping the connection open (like AutoSave). I don't know of any way to test notifications other than closing your browser, navigating away from the site or signing out and waiting a day or so to see what notifications show up in your mailbox.