There's actually a few problems here and no one simple fix appears to resolve it.
I've uploaded a new build to the download area with an updated set of files to try:
pp-inc.php
showcat.php
templates/feature.tmpl
templates/featurepal.tmpl
(If you use the vb3enhaced files, you'll need the feature.tmpl and featurepal.tmpl files uploaded as well from the vb3enhanced directory).
This was an attempt to bring over some thumbnail caching and it doesn't appear that I thought it out as well as I should have. I've put it back the way it was for now and I have it working on
http://www.photopostdev.com/classifieds/index.php
Download the latest build and update your files and let me know if that fixes it for you.