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Just to confirm, on a render I have going right now, after the "Indirect Lighting precalc" phase completed, Poser wrote a file named *.icache, leading me to think this is the light map.  I think when the render completes it will erase it.  I don't see any option to control this behavior.

Ah well, thanks. :-)
Seems it's not doing what I was hoping. One day, perhaps.