When I moved a friend's site from one server to the other, I made sure to change all the paths in wp_posts.
However, the post_image function I was using caused an open_basedir restriction error. I found out that there were still paths to the old images in the wp_postmeta table. When I fixed that too, I found that now all the images are inside the media library - meaning that the full-size image AND the thumbnail show up separately. Obviously, WordPress does not know that one belongs to the other.
Any ideas what caused this? And how to fix it?
I think the old version of the site was running WP-2.5 or 2.6 ... maybe the update step was too big?