My latest tests:

1- Using a two side square instead of one side square gives the same broken mesh rendering.

2- Using a thin cube instead of the square nothing is changed.

3- Increasing the depth of the cube so the mirror is left inside the result continue to be the same.

4- Changing any parameter in the rendering setting has no effect on the mesh crash.

5- Replacing the paraboloid mirror with a one side square mirror, the mesh is not more broken.

6- Refraction index bigger than one makes the reflected image to be more near (plane mirror)

7- Refraction index smaller than one makes the reflected image more far away

8- Refraction index of 0.2 duplicates the reflected image, weird !!!

9- Negative refraction index bigger than one have a magnifying effect.

10- Negative refraction index smaller or equal to one produce no reflected image

11- Using the paraboloid this time with refraction and a reflective square behind doesn't break the mesh and have a magnifying effect depending on the focal distance of the parabolid.

Conclussion.

The parabolid cannot be used, at least in Poser6, as reflective surface if is behing a refractive surface because it makes the mesh's reflected image  into pieces. I suppose that the same will happen with any surface that is not a plane.

Instead a plane surface used as a mirror can be used behind a refractive surface and doesn't break the reflected mesh.

LuxRender doesn't makes the mesh crash and behaves normally, pity that is very slow and negative refraction indexes doesn't work

 

Stupidity also evolves!