Yes, as far as I can tell, it has something to do with the double-sided polygons. Poser 4 is less sensitive to such things, but Poser 5 doesn't seem to like them, even with the old P4 renderer. No official fix as yet, although there is a simple workaround.

Plug your texture map into the Displacement channel and set it to a very small value (0.01). I'm not sure why this works. My theory is that the displacement manages to separate both sides of the polys just enough to avoid the effect.

Further reading:
http://www.renderosity.com/messages.ez?Form.ShowMessage=917912
http://www.renderosity.com/messages.ez?Form.ShowMessage=905904