Something to make you go "hmmmmm..."

I was trying to make this image using a bent-up bicubic patch, and
noticed some odd bright and dark spots on it.
If you have say, a single light source, a bicubic patch, and an object
between them, you can see the shadow of the middle object on the "dark
side" of the bicubic patch.

The pigment was a conventional color rgb < 1, 0, 0 > , with _no_
transmit or filter in it. Ambient was 0.0, and no other finish was
applied, no radiosity.

I took several looks at it, rotating the camera around and so on, and
noticed that there were bright areas on the (supposedly) dark side,
corresponding to where you'd expect a bright area on the illuminated
side.

It's as if the patch was transluscent, like ground glass, or something.
Not like filter or transmit, because light doesnt pass through it to
other objects, nor can you see through it.

If one bicubic patch is partly shading a second patch, the top one casts
its shadow on the second one, (as expected) and this shadow 

I tried placing two instances of exactly the same bicubic patch in the
same exact place, but the transluscent effect

The patch did not fold back in on itself or anything too outlandish.

Similar infinitely thin objects, like clipped planes, don't do seem to
do this.

I noticed this phenomenon in a Win version (3.something, Win95) of
POV-Ray, as well as with version 3.0.2a for Mac.

Any ideas?

-jr-

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