I surfed the demo page, selected the first product (Spiderman II) and then on the new page selected “Sin City”, “Spiderman II” and “Sin City” (in this order).
The first click on the back button led me back to “Spiderman II”, the second to “Sin City” - so far so good. The next click should have taken me back to the “Spiderman II” info page, but had me look at the product overview page, instead.