I don't know if following is a DO or Photoshop related problem:
In thumbail mode or when moving mouse over a PSD-Image in listview I can see the preview image. When opening the same file in the viewer a message appears "This layered Photoshop file was not saved with a composite image".
The "Compatibility" option saves a full-size composite of the image as part of the PSD, which allows thumbnailing application to do their job -- but at the expense of a much larger PSD.