No picture from elaps (sometimes)

[Jay Belanger <belanger@truman.edu>]

I have come across the following oddity in elaps, or perhaps the
oddity lies elsewhere, but shows up in elaps.
I noticed that sometimes, when elaps was run, the output would be a
white square with nothing in it.  For example, 


#include "epix.h"

main() {
  unitlength("1cm");
  picture(P(1,1));
  bounding_box(P(0,0),P(1,1));

  begin();
  
  triangle(P(0,0),P(1,0),P(0,1));

  end();
}

will produce a white square, but if the 1cm is changed to 1in, it
produces a triangle.  
Is there some reason for this?

Jay