Display "large" thumbnail with WP-Slimbox2

I really like the lean solutions Slimbox2 provides.

One of the features I’ve discovered on my blog running WP 3.5.1 and WP-Slimbox2 1.1.2 is that using the standard WP gallery feature, when the user clicks on one of the thumbnails, the “large” thumbnail (with the size defined in WP media settings) is displayed in the lightbox. E.g. here: http://beta.artagenda.com/norbert-moslang-capture-kunstmuseum-st-gallen
The trick is to put link=”large” in the shortcode: [gallery columns="4" link="large" ids=".., .., .."]

However, when I now wanted to apply the same to another blog (also running WP 3.5.1 and WP-Slimbox2 1.1.2), the same shortcode doesn’t work: The thumbnail always links to the attachment page, and clicking on the thumbnail there of course displays the full image in the lightbox :-/

Does anybody has an idea what code snippet might make the difference? I’d really love to implement this function on my blogs…

Thank you, Abstractus

http://wordpress.org/extend/plugins/wp-slimbox2/