Issue of page width with twenty fourteen theme

I have a site http://ift.tt/1A6nTdx based on Twenty Fourteen theme. I use heavily Mathjax-Latex. For some menus, like Topology, the page width is OK on an iPad.

For other menus like Analysis, the page width is schrinked compared to the width of the screen. This appears only a week before.

Do you have a clue of what can be wrong?

Thanks.