I have the same problem, and yeah, that's the site. Tapping the button to increase the font size just zooms the page in so now I have to scroll horizontally to read the content. Something on the page is preventing natural reflowing, I could probably figure out what if I was on my desktop. My hunch is it's the row of images.

It is because of this:

   .main {
      margin: 2em auto;
      width: 50em;
    }

So the whole page width just increases with the font size. I think they should have used max-width instead.

This also causes problems, when you resize your browser window.