I think this was patched just now. On my last visit a few minutes ago the bug still worked, now it removes any larger bits where the lines intersect.

Also, the code has been amended right where this comment is:

  // People like to draw shapes with kinks, which results
  // in part of the polygon being treated as negative area.
  // turf.unkinkPolygon can be used to find the kinks and
  // separate the polygon into multiple polygons at the
  // kinks, but it's a little fragile and hard to combine
  // into a single unkinked polygon. [...]