Dear Ferreters,
I've found a strange interaction between "set win/aspect=1" and "set mode linecolors". When both are present, the image produced with
pyferret -nodisplay -script example.jnl
is truncated on the right side!
If you swap the order of "set win" and "linecolors", the image is fine; or if you comment out one of them, the image is fine, too.