Artifact in rainbow demo

[remcoder]

The 4th outline seems to have a circular cutout or something.

If I only draw 4 outlines it can be seen that the white document background is now visible.

You can definitely make out a circle if we cut away some other paths

My hypothesis is that the algorithm has a round-off or equality error leading to an arc that is 360 degrees instead of (almost) 0 degrees.