[pstricks] 3D planes

[jmpapy]

Dear pstricks users,

I've the following problem:

These are two xy planes with different z coordinates (z=0 and z=0.3):  

\begin{pspicture}(-1,-1)(1,1)
\psset{Alpha=30,Beta=30}
\pstThreeDSquare[fillcolor=black,fillstyle=solid,linewidth=0.1pt]%
(-1,-1,0)(1,0,0)(0,1,0)
\pstThreeDSquare[fillcolor=blue,fillstyle=solid,linewidth=0.1pt]%
(-1,-1,0.3)(1,0,0)(0,1,0)
\end{pspicture}

Normally you should see a blue plane lying above a black plane.

Now if the order of the lines is changed:

\begin{pspicture}(-1,-1)(1,1)
\psset{Alpha=30,Beta=30}
\pstThreeDSquare[fillcolor=blue,fillstyle=solid,linewidth=0.1pt]%
(-1,-1,0.3)(1,0,0)(0,1,0)
\pstThreeDSquare[fillcolor=black,fillstyle=solid,linewidth=0.1pt]%
(-1,-1,0)(1,0,0)(0,1,0)
\end{pspicture}


we should see the same. But actually not. Because it seems that the 
plane are filled independently of their positioning in the 3d space. 

The main effect is that, it seems that the viewpoint has changed. But it 
can be very annoying if the figures are more complex.

Is it a bug or is it really necessary to order the code lines with 
respect to the positioning of the planes in the 3d space ?

thank you in advance

JM