Here's something strange: I'm going to design a new theme based on a blank html5 theme. Regardless of which blank theme i use, the plugin doesn't work on index pages.
I tried it with the toolbox theme for example. A html5 theme developed by Automattic.
The plugin doesn't work on my index page. The pictures are opened in a new tab. But when viewing the single post (single.php) it is working. I have no idea why this is happening. I experience the same problem in all other html5 blank themes i tested.
I also tried the plugin auto-thickbox, which worked out of the box on both index & single pages.
Maybe someone of you can help me?
URL for testing