There's a lot of great information here that I'll need some time to let sink in. But, in my case I think it has more to do with Poser not changing the pointer (to the texture file) when you apply your new MAT. In the Material Room watch the Color_texture node while you apply MATs. You will see that the texture name does not change. Yet if you click on image_source you will find that your new texture is now in the drop down list of textures to pick from. Pick your new texture from this drop down list and everything renders fine--- but of course that defeats the purpose of using MATs in the first place.