Hi,
I think it is a bug.
You can register it under the bug section.
I can provide you a workaround :
explode your shapes in faces ( for performance reasons ) : ( using TopExp_Explorer )
begin loop on your faces
convert the face to bspline ( using BRepBuilderAPI_NurbsConvert ).
Add the face in your HLR algo.
end loop on your faces
Compute the HLR
With this method, you should get a good result.
The only problem is that it is much slower than without converting to BSpline, but at least it's working fine ( I think ).
HTH.
Commenter-1
http://www.exotk.org