Quote - Did you try change square prop. If you use poser primitive 2 sided square can give weird results.

I am using one side square, so it has only have one face. I have tried with the square subdivided into many small squares, but the result was the same. I have not tried a two sided square with no welded vertices or a cube with some volume enclosured.

With LuxRender is working, but the problem is that is very slow and this makes very difficult to work. Poser is fast and so I can change some parameters and render, change and render, change and render. Within some minutes I have done a lot of experiments, this cannot do in LuxRender.

Stupidity also evolves!