There is caching going on between the web server and your web browser. Sometimes your browser thinks that you're going back to a page you were previously on and displays it from memory - rather than ask for a new copy from the web server. Usually, if you force a refresh (some browsers call it reload) it will request and display an updated copy of the page. It can be annoying at times. I've thought about disabling it, but it really adds to the performance of the site - especially as we get more people using it.