It's not exactly a bug, it's a weak part of Poser's renderer design.  In the big dog renderers, you can selectively control whether objects are included in GI, reflection (and what depth of bounces for each of those, separately) and whether THIS object is illuminated by THAT light.  Also, transparency and alpha are treated completely separately in other applications, whereas Poser treats them the same (which is why no colored shadows through transparent objects).  The fact that Poser Indirect Lighting occlusion shadows don't handle transparency well is another big flaw.  Pretty sure none of these things can really be worked around at all in Poser.

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