[pstricks] centereing / psmatrix

[Bernd Brandt]

Dear group,

For some time i have been using psmatrix.
Suddenly i notice two things:
1) The node-connections (arrows) are NOT centered with respect to the box.
2) If i include the psmatrix in a pspicture environment \center does not work.

Has anyone a solution to these 'problems'.
I am esp. surprised that the node connections are not centered with respect to the boxes; they are just offset to the right.

Below the example. I hope someone is able to help me.
Kind regards,
Bernd

\begin{figure}
\center
\begin{psmatrix}[colsep=1,rowsep=1,mnode=r]
	[name=S] \psframebox{Substrate} \\[0pt]
	[name=E] \psframebox{Reserves} \\[0pt]
	[name=V] \psframebox{\shortstack{Structural Biomass Growth
	\\ ~\\ Maintenance }}
 \end{psmatrix}
  % Node connections
  \psset{linewidth=1pt,nodesep=5pt,offset=4pt,arrows=->}
   \ncline{S}{E}\naput{assimilation, $j_{EA}$}   
   \ncline{E}{V}\naput{utilization, $\dot{\jmath}_{EG} + \dot{\jmath}_{EM}$}
\caption{\label{fig:2:frame}}
\end{figure}