Comment 10 for bug 487052

running Windows XP and Inkscape 0.48.0 r9654 (Aug 16 2010), I get the attached file, which appears to be okay. (Not sure if the precision of the rendering is sufficiently good.)

could you try the latest version and see if it helps. The source code is hpgl_output.py, available at : Bug 600472, comment 13.

while doing the test I ran into a separate bug. If I select "Mirror Y axis", I get a Python crash with the message:
ValueError: invalid literal for float(): 100%
apparently caused by the presence of the % sign. Will try to come up with a patch for that shortly.