My program is offseting and linear_extruding this object with various
thicknesses and differences one from another. It generates a broken object
("Object may not be a valid 2-manifold") and I don't understand why.
Re: OpenSCAD generates non-manifold objects when importing .svg
The "does not happen with single hard object" is just an illusion as
the linear_extrude of 2d geometry does not involve the CSG engine
(this is not really advertised but sort-of visible by the different
As the problem goes away when adding offset(0.1) to the differenced
part, I suspect it might be an overlap at the sharp edge at the top.