Incorrect results of model.combine

Hello,
I came across a problem with a strange behaviour of model.combine. I have a circle and a polygon made of lines, and when I try to subtract the polygon from a circle, then a couple of lines stay visible outside of the result shape.

var circle = { 
  type: 'circle', 
  origin: [-122, -154],
  radius: 402.7,
  units: 'cm'
 };

var modelCircle = { paths: { myCircle: circle } };

var line1 = { 
  type: 'line', 
  origin: [-500, -399], 
  end: [-499, 201] 
 };
 var line2 = { 
  type: 'line', 
  origin: [-499, 201] ,
  end: [-670, -136]
 };
 var line3 = { 
  type: 'line', 
  origin: [-670, -136] ,
  end: [-500, -399] 
 };

var modelLinien = { paths: { myLine1: line1, myLine2: line2, myLine3: line3 } };

rootModel = m.model.combineSubtraction(modelCircle, modelLinien);

// same result
rootModel2 = m.model.combine(
            modelCircle,
            modelLinien,
            false,
            true,
            true,
            false
        );
		
var svg = m.exporter.toSVG(rootModel);
document.write(svg);

Start by running the supplied model.combineSubtraction example and inspect the model.combine and exporter.toSVG entry points. Compare the subtraction result with the SVG output to determine where the stray polygon lines remain. Done means subtracting the polygon from the circle produces no visible lines outside the resulting shape.