It isn't blocked. It's because in that setup, the IBL is very dark. Look at the ground contrast between lit and shadow. P8 renders like that, too, when the IBL is not contributing much to the lit area. A 20% decrease in something that is only 20% to begin with is a 4% decrease in luminance.

Poser 8 will produce a similar appearance if you have a very weak IBL. The attached image above is from P8.

This is one of those cases where trusting your eyes is a mistake. There is an occlusion shadow all around the ball, even in the lit areas. How we perceive it is very different than what it is. You must not trust your eyes so much.

For example, look at this render.

A and B are exactly the same color. Perhaps you don't believe it? Sample the colors in Photoshop. They are both RGB 120, 120, 120.

When we observe a highly simplistic 3D scene with strong light and shadow cues, our brains do strange things.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)