Strange behavior when polygon is closed

[AlgoTrader]

When polygon is not closed, everything is OK
When polygon is closed (firstPoint==lastPoint), the intersection is weird. Weird means

[AlgoTrader]

When remove (just drop) the last closing point, the result is:

[NTag]

I exactly face the same issue. The following code (should) computes the intersection between two basic squares.

console.log(greinerHormann.intersection(
  [
    [0, 0], [0, 1], [1, 1], [1, 0], [0, 0]
  ],
  [
    [0.5, 0.5], [0.5, 2], [2, 2], [2, 0.5], [0.5, 0.5]
  ]
));

And instead of returning [[0.5, 0.5], [0.5, 1], [1, 1], [1, 0.5], [0.5, 0.5]] it returns

[ [ [ 1, 0.5 ],
    [ 1, 0 ],
    [ 0, 0 ],
    [ 0, 0 ],
    [ 0, 1 ],
    [ 1, 1 ],
    [ 1, 0.5 ] ] ]

which corresponds to the first square...

[srt19170]

Ditto, I've run into this as well.

[hefler]

I think what you guys are facing is a Leaflet issue.
In Leaflet polygons should not have the same first and last coords.

From the docs (https://leafletjs.com/reference-1.4.0.html#polygon)

A class for drawing polygon overlays on a map. Extends Polyline. Note that points you pass when creating a polygon shouldn't have an additional last point equal to the first one — it's better to filter out such points.

[Xrayez]

In Leaflet polygons should not have the same first and last coords.

I'd go as far as to say that this is how other polygon clipping algorithms work to be honest. For example, in Clipper you can add both polygons (closed) and polylines (open), and this is explicitly distinguished via closed = true parameter when adding paths.