PBR playground example different depending on what was viewed before

I see something different if I go directly here:

http://babylonjs-playground.azurewebsites.net/?28

to if I, say, go here:

http://babylonjs-playground.azurewebsites.net/?12

then choose PBR from the drop-down box. When I do the latter the four meshes are semi-transparent.

I've managed to reproduce this on both Firefox and iPad. I'm guessing that one or the other of the playground entries is setting some global state that it shouldn't?

By the way, the "wrong" way is actually quite an interesting effect: the balls look a bit like very delicate glass, or soap bubbles. It might be worth adding a comment, or bool var, to say how the effect can be reproduced.