the original image posted at the top is definitely incorrect and certainly can't be explained by TIR effects.
I have to desagree
Can you demonstrate what you say ? I can demonstrate I think this is TIR effect
I missed the edit before replying first so, as I've got nothing better to do at the moment, here goes...
There is plenty of light from the sun being transmitted through the glass (see 1)
There is plenty of light being transmitted through the glass to the camera (see 2). You might argue that what we see in the glass is a total reflection but this can't be the case, otherwise there woudln't be a dark patch at 3.
From the above, there's clearly little or no TIR occurring at either the viewing or dominant illumination angles.
Now look again at 3. From 2 we know that the viewer can see plenty of details through the glass and that the contrast of those details isn't significantly affected. In which case, why is the detail of the shadow/ground (as viewed through the glass) not apparent?
And while I was typing this, I just read your last response ... yes, I'm talking about why the shadow viewed through the glass is invisible.
There appears to be a TIR caustic just below the glass (and one behind it) which would be the sun light entering the top of the glass and bouncing around a few times before emerging from the bottom. This looks like it's a correct TIR effect which is missing from the PT render for some reason (probably because PT is less efficient at finding rare caustics ... TIR is a red-herring in this case, it just makes it less likely to find the caustic but it would show up eventually).
Re: tonemapping ... I don't think this is the problem, otherwise the PT render should show the same bug. I've never seen tonemapping so dramatically change the contrast of a detail when the original image isn't particularly high dynamic range to start off with.
Maybe we were indeed talking about different things