Back button "conflict" between unplatform and content player

[coleshaw]

When you click on the sidenav in content player, the iframe source changes as expected. However, if you use the browser's Back button to go to the previous ePub page, only the iframe changes (so the side nav doesn't update to reflect the "previous" page). If you click a second time, then the side-nav updates.

I suspect this is because the focus shifts to the iframe on click of the sidenav, so the first "Back" button click causes the iframe to go back, not the whole unplatform window.