My guess is that this is a bug.
If we click on the Category link on the home page, it should be sorted by newest/latest uploaded photos, but for some categories, there are a few photos in the beginning are not from the latest photos, but some older dates.
Here are a few example page: http://www.photozo.com/album/showgallery.php?cat=504
First few photos are from August, 2005, followed by latest September photos. http://www.photozo.com/album/showgallery.php?cat=502
First few photos are from May 2005, followed by latest September photos.
Is there something wrong, or is this the way it's supposed to be?