When I edit an existing psd file, then close and save, the thumbnail does not update. If I save it to a different file name, it is correct. These two were the same file, 'a' was saved under a different file name.
The change I made was to warm it up a bit. You can see the original thumbnail (attachment) has not changed. The preview is not correct, either. When I do a save as in PS and go back to the contact sheet, it briefly displays the correct thumbnail then reverts to the old one.