I found the Shadow Catcher in Poser 12 reflects the light in the scene when it shouldn't.

Here is an example of the problem.

I created a scene that only has an HDR file in the Background material for the light source.

I set a square prop as the shadow catcher, (Checked Shadow_Catch_Only)

As you can see, Victoria is brighter like something beneath her is reflecting the light.

Here is the scene with the Shadow_Catch_Only unchecked.

When comparing the checked and unchecked images, Victoria is lit up the same.

Is there another way to setup the shadow catcher? If not, this is a serious bug and a big disappointment. A proper shadow catcher was the feature I really wanted.