If you load a two-sided square prop - 2 polys, 8 verts - and render it, you get this off the wall pattern from the diffuse_color node. 
Same result and same pattern on both sides of the square.

However, if you use the alternate_diffuse node, it renders a complete square just like one would expect.

Whassup!!??

 
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Poser/firefly doesn't like double sided polys. apparenly it gets confused as to which side it should be showing. You can fix this by either go to materials and check the "normals forward" box or use one sided square prop.

But it's only with the diffuse_color node. 

Alternate_diffuse renders just fine... There's apparently something else going on here.

 
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That answer really sucks!

 
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Sucky or not, this is definitely typical.  Since v5, Poser has given
this strange barcode or alien checkerboard look for two -sided facets.
It's sort of intermittent and irregular. 

Some people have said you can fix it by turning on displacement for the 
texture, but it's better to get rid of the two-sided facets.  Either change the 
model so it has two actual opposite-facing sides, with a slight space 
between, or make it strictly one-sided.

Quote - But it's only with the diffuse_color node. 
Alternate_diffuse renders just fine... There's apparently something else going on here.

Its only with double sided polys. Alternate_diffuse is processed in a diffrent way so it's not really a suprise that it looks diffrent.

apply a specular in the alternate_specular and it has the dashes too. a bit more subtle but still there.

Normals_forward seems to work if your not using alternate_ settings.

Pluging a simple color into the displacement and setting it really low (0.0001 or so) seems to fix it every time.