lfys on "2013 theme has whitespace on the right, just outside small screen"

Hi.

My WP 3.6 testsite with Twenty Thirteen theme shows a white area on the right, just outside the screen, when viewed on a smartphone.

I stripped it of everything I could think of causing the problem. Still, viewing for instance this page on my Android phone or with an iPhone simulator, the problem persist.

I'm running out of ideas. Can anyone with some experience take a quick look?
Thanks.