What caused this sudden bug in my parallax zoom?

I setup a page here last year based on the parallax at Beercamp. It was the first time I saw the technique and really enjoyed it.

Recently, I noticed I've lost the ability to select any objects on the deepest (bottom) layer. For example, clicking the spinning top in Beercamp returned you to the start of the page. My page is stopped doing this as well, just out of the blue.

What could have changed between both pages to cause this?