I rendered the same scene with LuxRender and is working without any problem and didn't break the mesh as Poser does.

The plane with refraction index combined with a paraboloid mirror behaves as a magnifying glass. You can change the maginification changing the refraction index of the plane or the focal distance of the paraboloid mesh.

If the plane is set with a refraction index = 1.0 the plane turns invisible and the rendering with or without the plane gives the same result, what is correct.

Stupidity also evolves!