Lightbox of pretty photo doesn't pop up to its full size only on mobiles' landscape mode

I have a responsive website, but the lightbox of pretty photo (due to some custom coding) doesn't pop up to its full size only on mobiles' landscape mode. So how do I let all mobiles (tablets are fine) to stay on the portrait mode even in the landscape position? (The site has visual composer.)

Here's a link: http://anjandasdesign.com/mw-mag/ Try opening it on a mobile in the landscape mode. Perhaps you could help me out here?