When I first started using this plugin clicking on the thumbnail images (on a page with the shortcode) would open the full size image in it's own small window above the page, like a popup. You could then just close that window and continue browsing the images. Now they are linking to a new page, and you have to hit the back button to get pack page with the gallery.
Nothing has changed with the galleries, or the plugin, and I have not done any major changes with the site, but it is possible that some small change I made affected this.
Any ideas of what may have changed the way it opens the images?