plot3d and autoscale



I am having a most weird problem with the default 3d plot viewer (Schelter's)
 under maxima-cvs: upon issuing the command

Plot3d([4*(1-z^2)^(1/2),x,z],[x,-%Pi,%Pi],[z,-1,1],['TRANSFORM_XY,POLAR_TO_XY]);

I get a pretty picture of a sphere (!), which is not quite what I
expected. It seems and appears that a
transformation is applied on the image in such a way as to have
the scale on the z-axis to be exactly 1/4 of that on the xy plane
(this is also what I see when looking at the coordinates of the points).
Alas, altering the "config" options does not change the output, and
I am not so sure about what to tweak/change in omplotdata in order to
get the behaviour I would like. Any clues?

Thanks in advance,
 luca giuzzi

P.S.
 I have seen that the direct-to-postscript rendering seems to be broken.
 The error I get (from the same command as above) is 

Last error is: >> argument to * should be a number: NIL <<

a backtrace shows that the culprit should be somewhere near  "PS_AXES",
since the last frames which have been called (before the break) are

[10]> #<SYSTEM-FUNCTION *> 2
[11]> #<COMPILED-CLOSURE $ROTATE_PTS>
[12]> #<COMPILED-CLOSURE $PS_AXES>
[13]> #<COMPILED-CLOSURE $PLOT3D>

I shall try and look about what might be done about this, but,
before attempting further investigation, I would like again to inquire
if there is somebody which is already working on it.

thanks again,
 lg
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