Member Rara Avis
You have the ever-so common caching bug.
Go to the Member's Area in the menu at the top of the page, then click on the Troubleshooting Guide link. There's an article under Common Problems about caching, called "I can't see the post I just made!" In your case, of course, you can't see the posts someone else just made. But the cause is the same, as explained in the article, and the resolution (where possible) is also the same.