I also can reproduce the bug.
This is something I would like to investigate. It looks an interesting work so I can learn some of the FreeCAD internals in order to do more advanced work in the future.
I intend to have something delivered before May 1st, or an answer for you that I coundn't find the bug, so you have the rest of the year to delegate that to a more experienced developer.
Is it ok for you?
References to documentation about that are welcome.