Unexpected behaviour for combineSubtraction

Loving this project so far - I'm planning on using this for my CNC-designs going forward. In order to do that I will need to understand the library, and I'm currently struggling with the combine methods. I'm trying to "cut out" a part from another part. but not all paths are removed.

See the example below. I'm trying to cut out one corner from the box, but the only paths that are removed are the ones from the corner, not from the box itself. Those two paths (ShapeLine2 & ShapeLine3 on the 'box') are instead split into two paths each..

I would have expected to end up with an "L" shaped model below. What am I doing wrong?

var makerjs = require('makerjs');

var lShape = {
  models : {
    toprightcorner: makerjs.model.move(new makerjs.models.Rectangle(50, 50), [50, 50]),
    box: new makerjs.models.Rectangle(100, 100)
  }
};

makerjs.model.combineSubtraction(lShape.models.box, lShape.models.toprightcorner);

var svg = makerjs.exporter.toSVG(lShape);

document.write(svg);

Thankful for any feedback.

Start at the combineSubtraction entry point and reproduce the supplied Rectangle example before inspecting how the box and corner paths are processed. Compare the generated SVG with the expected L-shaped model; done means the corner is removed from the box without leaving the box paths split incorrectly.