What if you're seeing the cached thumbnails created by the last version of thunar that created thumbnails? To tell, look at the dates in the ~/.thumbnails directory, specifically the large and normal subdirectories.
You could also try deleting all of those and see if thunar will regenerate _any_ of your thumbnails.
IIRC, the thumbnailing system in xfce/thunar underwent something of an overhaul and filetype-specific thumbnailers now have to be written that know how to transform each type of file into a thumbnail of itself.
However, don't place too much credence in what I just said as I don't know exactly how long that system has been in place...
Last edited by jamesf; 08-11-2012 at 05:22 PM.
Reason: corrected directory path.