I took a look at the site last night and saw the issue you were having. I installed the plugin on my testing site and could not duplicate the issue. For some reason, the html that is output is telling the other thumbnails to not display.
I logged in today, and noticed they came out with an update to the plugin. I would suggest trying to install that and see if the problem gets fixed.
What plugins do you have installed? I’m seeing the plugin working on another install, so maybe there is something that’s conflicting. I can try and install them on my setup and see what happens. Is the test subdomain a separate install from the main site?