It's not exactly 'broken'. When you go to the home page it geolocates you, and then forwards you to the correct home page for your location. Admittedly it then makes it feel a bit broken...
Putting my browser in a state where the back button doesn't let me leave the site is the definition of breaking the back button. Worse than those back button pop-ups that only fire once (this is like a popup that fires every time). Definitely check out window.history.replaceState as mh- suggests.