It doesn't break it as much as it very liberally adds states for all the changes you make in the page, to the point it's hard to see anything in the back history except what you've done on that page. Go far enough back and you get back to the prior page though. It was sort of annoying.

Most browsers these days give you a list of your history when you hold down the back button. Useful for sites that do this or to get out of redirect loops.

But I agree, the sites behaviour is annoying and far from ideal.

It would be more palatable if going back updated the UI state to the previous location of the country you were dragging around, but this doesn't seem to work (at least not in Firefox).

It's a cool project but this Back button behaviour is incredibly irritating. I ended up having to click the button about 50 times to get back here to the discussion.