mj,
I checked the logs and your browser is sending two requests to visit the thread. This indicates a possible double-click on your part. Are you sure you're not clicking on the link twice?
You visited the thread at 2:47:09 (9 seconds after the minute) and again at 2:47:10 (1 second later). The first hit would have told the server you've seen the thread and then on the second hit, the server thinks you've seen all the posts and thus there is nothing new for you.