[pstricks] Why is my picture moving?

[Christoph Bersch]

\documentclass{beamer}
\usepackage{pstricks}

\begin{document}
\begin{frame}
     Test
     \begin{pspicture}(0,0)(2,2)
         \uncover<1->{% <----
             \only<2->{\psset{linecolor=lightgray}\lightgray}
             \psline(0,0)(2,2)
             \rput(2,0){test}
         }
     \end{pspicture}
\end{frame}
\end{document}

I only added the %-sign after the opening brace of \uncover

Christoph