I set up as you did with the default IBL SUN RIGHT light in Poser 6. I dont get that effect. However I did change light sets from the IBL to the "old" light array type set and got the effect you posted above. I say its the way this wonderful texture interacts with the lights.

"Few are agreeable in conversation, because each thinks more of what he intends to say than that of what others are saying, and listens no more when he himself has a chance to speak." - Francois de la Rochefoucauld

Intel Core i7 920, 24GB RAM, GeForce GTX 1050 4GB video, 6TB HDD space
Poser 12: Inches (Poser(PC) user since 1 and the floppies/manual to prove it!)