[pstricks] question about pst-solides3d: projection on a plane

[Clemens Schäfermeier]

dear pst users,
i can't see why it is possible to project the xsin function to the first 
plane "monplane1" but it isn't to do this projection with ysin on 
"monplane2". any hint is greatly appreciated!

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\documentclass[a4paper]{article}
\usepackage{pstricks,pst-solides3d}
\begin{document}

\psset{unit=1cm,viewpoint=20 60 20 rtp2xyz,lightsrc=28 55 25 
rtp2xyz,Decran=20}

\begin{pspicture}[showgrid=false](-5,-5)(5,4)

\psset{solidmemory}

\defFunction[]{xsin}(x){x SIN}{}{}
\defFunction[]{ysin}(y){}{y SIN}{}

\psSolid[object=plan,
definition=equation,
args={[1 0 0 0] 90},
action=none,
name=monplane1]
\psProjection[object=courbe,
plan=monplane1,
linecolor=red,
range=-3 3,resolution=720,
function=xsin]

\psSolid[object=plan,
definition=equation,
action=none,
args={[0 1 0 0] 0},
name=monplane2]
\psProjection[object=courbe,
plan=monplane2,
linecolor=green,
range=-3 3,resolution=720,
function=ysin]

\end{pspicture}

\end{document}
%%%%

kind regards
clemens