IMHO: The 2 horizontal and the 2 vertical segments aren't selected.
They are displayed black on white.
Compare this to the ellipse left high, that is displayed faint red on white.
This shape is filtered out the selection as it is not a line segment.
From the described method used that would indeed result in a 3-point circle when selected as one whole.
Start- mid- and endpoint. The same happens with the tessellated ellipse.
Already explained that the startpoint of a closed polyline from selection can be at random.
This would be the part where Brock wants to filter out parts that are not uniform in length ...
That is, if tessellated curves are made up of such uniform segments.
I came across examples where you have a fixed length + 1 segment for the remaining part.
Other Arc2Segments methods may split it up at fixed orientations.
For the moment I have no time, nor the necessity to look deeper into this.
I also foresee ambiguous situations.
You could always try to reach him by PM.
His last post on the QCAD forum is dated: Mon Apr 19, 2021 9:12 am