[XeTeX] centering using geometry package

[Daniel Greenhoe]

I am using pstricks to produce a book cover. Before sending it off to
the print house, I want it "exactly" (or with a very tight tolerance
anyways) centered on an A3 sized page. To help with that, I use the
geometry package. In an effort to check if everything is really
centered, I use the "showframe" option. I have reason to believe it
may be working correctly. But one thing that concerns me is that there
is an extra vertical line that appears about 2.5mm to the right of the
text body frame box. Can somebody tell me, what is that line? Can I
eliminate it somehow? Here is a somewhat minimal example:

\documentclass{book}
\setlength{\parskip}{0mm}%
\setlength{\parindent}{0mm}%
\usepackage{geometry}
\usepackage{pstricks}
\usepackage{pstricks-add}
\geometry{
  xetex,
  paper=a3paper,landscape,
  centering,twoside=false,
  ignoreall,
  textheight=284mm,textwidth=400mm,
  truedimen,
  showframe
  }
\begin{document}%
\psset{unit=1mm}%
\begin{pspicture}(-200,-142)(200,142)%
  \psframe[fillstyle=none,linestyle=dotted,linecolor=blue](-200,-142)(200,142)%
\end{pspicture}%
\end{document}%

Many thanks in advance,
Dan