P3dO Explorer is well worth getting, in my opinion; but if I had to guess, I'd guess that its partial pose feature uses the same mechanism as applying one within Poser and would be subject to the same bug. The developer (Yarp) is approachable and friendly though, so I'd encourage you to ask him if this is a deal breaker for you.

My Poser 7 is patched to SR3 - the light keyframe bug is not fixed in that release, but thanks for the suggestion. It doesn't bother me too much since I don't use the animation features in the traditional way anyway; my default condition is keyframes on every frame, and I usually have the animation palette open somewhere on my screen since it's integral to my workflow.