It's because it's YOUR topic and you've read it.
Like this topic. Before you read this post, you could see it by clicking on Main from the Home page.
But it wasn't until someone else posted to it that it showed up (for YOU) on the Recent, Watched and Unread listings as well.
We could all see your first post in the topic on our Recent/Unread listings even though you didn't. ;-)
So, no problem, and you're not doing anything wrong. It's just how the board software operates. Pretty standard.