That is crazy. It's apparently the default behavior of a WordPress plugin I'm using, ostensibly to make the site more readable on mobile. Thanks for telling me.
It's WPtouch - that behavior is inexcusable. I've disabled the plugin so you shouldn't see the problem any more (although it will also not look quite as nice on mobile, unfortunately).
Thanks for taking the complaint seriously :) I quite enjoyed the article but I have knee-jerk reactions when sites do this.