This is a tough one to explain, but let's see if I can make sense. Unfortunately, I'm running the site of my local machine (for now), so I can't show what's happening.
I've got the main page of the blog set up to just show excerpts of all posts. When I go to the Single Post page (either by clicking the title or more... ), it shows the text of my oldest post at the bottom of the screen, underneath the template. It's basically a repeat of the post (which does show properly), but outside the template.
If I delete that oldest post, the "new" oldest post then appears. It doesn't matter which post I'm viewing, they all show the oldest at the bottom.
I have no plug-ins enabled, and this is happening on 4 different themes, including the WordPress default.
Has anybody seen this before? Any suggestions for me?