[tom]

Mauro, the effect you're seeing is called Snell's Window caused by Total Internal Reflection (TIR). Here's the explanation:
http://en.wikipedia.org/wiki/Snell%27s_window
So, your view gets blocked when you meet the critical angle...

The internal reflection on the facet of glass gets propagated on the other faces. These reflections occur when the light can't escape from the glass body due to critical angle. It's also why and how all those diamonds look brilliant. They are precisely measured cuts trapping light inside the object as much as possible.

Look, here's how I demonstrate it by replacing the backface with a solid coat. I'm sure you've seen these kind of decorative glass or acrylic sheets having color edges.
(The video file is 150 MB, so it will take some time to appear.)

[hatts]

Ah, this feels like the resolution to a cliffhanger. Thanks Tom

[Mauro]

Tom, thanks for the feedback. I started looking myself into it and it makes sense that the internal reflection would bounce around due to the non parallel faces. Your movie illustrates well some of what is happening.