Wow - you should try unplugging your computer's power cord from the wall outlet, and see if your computer continues to run! :)
Is is possible that you're using a DB for your main server, and the posts in App_Data\posts are older ones before you may have switched to DB storage?
Have you customized the blog in any way? A customized blog could be setup to retrieve remote posts or remote data and display that data along with the other posts, without saving them in App_Data\posts.
Do you have the blog installed in a sub-folder? If so, and it's running within the same application as the parent folder, then you could check to see if there's an App_Data\posts folder in the parent folder where the posts might be coming from.
You can try restarting the blog on the main server, and see if these posts continue to appear after a restart. You can restart the blog by making any change to the web.config file (add a space, etc). When you do this, any data in memory will
get cleared out and the data in App_Data will get re-read.