Paper.js: Boolean path.subtract with { insert: false, trace: false } doesn't work well on rectangle with and without radius

[SteamWind]

Description/Steps to reproduce

Create a Rectangle Path with radius, apply a subtract(anyShape, { insert: false, trace: false }) to the bottom left edge.
It doesn't work with normal rectangle too. It appens with when you subtract a shape to the bottom left corner.
The path doesn't subtract well. It cut the path in intersections but doesn't remove it.

Link to reproduction test-case

Reproduction sketch

Expected result

It should remove the path under the subtrahend shape:

Additional information

PaperJS V 0.12.3

[SteamWind]

Hey, we found a weird thing that fixes the bug. If you split the base shape, this doesn't happen:

path.splitAt(0);

Then the path is opened. This should be related to this.

Here is the sketch from the original issue with the quick fix