Just installed the 4.1 updater, and it appears after a quick light-lab the results are now useable. The results are, however, absurd. I'll have to run a more complete light lab to create a full truth-table, but what appears to be the new behavior in 4.1 (OSX), is that objects either DO inhibit passage of skylight, or do NOT. I've placed the transmap both in transparency channel and in alpha channel, and in both cases the object became invisible to the skylight -- regardless of it's own visibility. I'm working now to see if this behavior translates to a Poser import. So far, I've discovered Transposer uses neither alpha nor transparency channel per se, instead creating a mixer between two multi-channel shaders -- one with transparency on, the other not.