Hi Jeremy,
Looking at the source for your site all I see that would be causing this behavior is the admin parameter "Include Main Image in Gallery". Can you double check that this is set to true?
your first image looks like this:
"images/products/tes7133.jpg" rel="lightbox"
and the additional image looks like this:
"images/products/tes7133_01.jpg" rel="lightbox-g"
the important part is the rel="lightbox"
when the "include main image in gallery" mode is enabled
the first image should have re="lightbox-g" in the code.
therefore linking all of the images together
daniel
Bookmarks