John,
It appears that this example
> > plot3d([u,v,2],[u,-3,3],[v,-3,3]);
triggers a bug in Gnuplot 4.0. Someone asserted (in comp.graphics.apps.gnuplot)
that it is fixed in 4.1, but that version is still in progress and not released.
Here are 2 ways to work around it.
Disable gnuplot_pm3d (3-d shading) option.
Surface is represented as a grid without shading.
plot3d([u,v,2], [u,0,1], [v,0,1], [gnuplot_pm3d, false]);
Assign a color range for shading. (It appears that this is the bit that
Gnuplot 4.0 goofs up when the function to be plotted is constant.)
plot3d([u,v,2], [u,0,1], [v,0,1], [gnuplot_preamble, "set cbrange [0:10]"]);
Maybe Maxima should attempt to detect this situation and compensate
automatically. If anyone has a suggestion, I'll be interested to hear it.
Maxima can include Gnuplot 4.1 when it is released but til then probably
Maxima should try to work around the problem.
About the failure of the openmath format, that's a separate bug
and I don't have any ideas about how to fix it.
best
Robert Dodier