Hi macray,

> => suddenly 2 more points are added that I don't need. Why is that?

It's because the curve filleting code internally fuses together G1 pieces into a single bspline, which involves degree elevating the different segments to all have the same degree as the existing arc which is degree 2.

I've added that to my todo list to rework how the corner fillet processes stuff to avoid doing that, thanks for reporting it.

- Michael