I don't understand PMP::detect_sharp_edges

[stla]

Hello,

Below is an astroidal ellipsoid on which the edges detected with PMP::detect_sharp_edges with angle bound =90 are shown in red. As you can see, some "borders" of the astroidal ellipsoid are not considered as sharp, they're not red. However they should be considered as sharp, because of the symmetries of this astroid ellipsoid: the "borders" are the same up to the symmetry, so if there's a red border then all borders should be red. Why some borders are not red?

[stla]

I see. It was not so symmetric, because the number of subdivisions I took to construct the mesh was not a multiple of 4.