When I imported the 4-vertex/1-face OBJ into Poser 9 and rendered with default lights (Four lights: One Diffuse IBL with AO; Two spots with depth-mapped shadows and AO; One infinite with depth-mapped shadows) I got an odd effect:

The plane seems to be translucent when viewed from the 'wrong' side - this appears to be what bagginsbill referred to on page 3 of the "waxy leaf" thread - to paraphrase, the completely ordinary lighting of the built-in diffuse node (or any diffuse node) conveys front lighting to the back. (but does NOT convey back lighting to the front).

Here's what we see looking at the 'right' side of the setup where I see the shadow:

I think we only get see two shadows here from the infinite and the spot close to it. It looks like we saw both those shadows when viewing from the 'wrong' side earlier.

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The 3Dcheapskate (also available in DAZ and HiveWire3D flavours) occasionally posts sensible stuff. Usually by accident.
And it usually uses Poser 11, with units set to inches. Except when it's using Poser 6 or PP2014, or when its units are set to PNU.