[pstricks] Strange 3D behaviour with viewpoint 1 -1 1

[Georg Verweyen]

If you have chosen {viewpoint=1 -1 1} and you get strange rotated lines 
in 3D (wich are in fact not rotated at all, while all the rest /is/) 
just change the viewpoint slightly. The example producing the fault, 
wich I posted earlier, can be fixed by setting \psset{viewpoint= 1.0001 
1.0002 1.0003} for instance. I exchanged some data and pictures with 
Herbert, we tried lots of viewers and different systems pstopdf and 
VTeX, with a bunch of different results, faults in display and/or 
printout, strange colour-shifts - a big variety of faults. It probably 
is a little bug in pdf itself.
Hoping this saves someones time and nerves oneday,
Georg