The list shows the latest posts in a chronological order, not necessarily the newest posts since you were last here. If you manually log yourself out of the website, when you return ... it is supposed to show only the newest posts since you were last on here when you click on "New Posts". Your computer cookies keep you logged on for hours after you have left the site so that you don't have to log-in every time that you come back.
Feel free to just send me a PM if you have questions about the site. Thank You