No lightbox on iPhone

Your demo website gives a gallery. When I click a photo on my iPhone I get a lightbox and I can click through the series.
With my own galleries that doesn’t work. The site is still responsive, but a click shows the photo full screen and no next button available. http://www.jaapmeijer.com/uncategorized/test/
For settings see screenshot at http://www.jaapmeijer.com/images/knipsel.jpg

http://wordpress.org/plugins/responsive-gallery-grid/