Cone surface returns wrong v derivative

Here is the C++ test code. It was built under Ubuntu with: g++ main.cpp -I/usr/include/opencascade -lTKG3d -lTKernel -lTKGeomBase

#include <Geom_ConicalSurface.hxx>
#include <GC_MakeConicalSurface.hxx>
#include <GeomLProp_SLProps.hxx>
#include <gp_Pnt.hxx>
#include <Precision.hxx>
#include <iostream>

gp_Vec DN(Handle(Geom_ConicalSurface) s, double u, double v, int Nu, int Nv)
{
    // Copied from ElSLib::ConeDN() and applied the needed fix
    auto ElSLib__ConeDN = [](const Standard_Real U,
                             const Standard_Real V,
                             const gp_Ax3& Pos,
                             const Standard_Real Radius,
                             const Standard_Real SAngle,
                             const Standard_Integer Nu,
                             const Standard_Integer Nv)
    {
       gp_XYZ Xdir = Pos.XDirection().XYZ();
       gp_XYZ Ydir = Pos.YDirection().XYZ();
       gp_XYZ Zdir = Pos.Direction ().XYZ();
       Standard_Real Um = U + Nu * M_PI_2; // M_PI * 0.5
       Xdir.Multiply(cos(Um));
       Ydir.Multiply(sin(Um));
       Xdir.Add(Ydir);
       if(Nv == 0) {
         Xdir.Multiply(Radius + V * sin(SAngle));
         if(Nu == 0) Xdir.Add(Pos.Location().XYZ());
         return gp_Vec(Xdir);
       }
       else if(Nv == 1) {
         Xdir.Multiply(sin(SAngle));
         Zdir.Multiply(cos(SAngle));
         Xdir.Add(Zdir);
         return gp_Vec(Xdir);
       }
       return gp_Vec(0.0,0.0,0.0);
    };

    Standard_RangeError_Raise_if (Nu + Nv < 1 || Nu < 0 || Nv < 0, " ");
    if (Nv > 1) {
        return gp_Vec (0.0, 0.0, 0.0);
    }
    else {
      return ElSLib__ConeDN(u, v, s->Position(), s->RefRadius(), s->SemiAngle(), Nu, Nv);
    }
}

int main()
{
    double u = 5.23290599890759;
    double v = 5.06498283391571;
    GC_MakeConicalSurface gc(gp_Pnt(0,0,0), gp_Pnt(0,0,10), 2, 4);
    Handle(Geom_ConicalSurface) cone = gc.Value();
    gp_Vec du = cone->DN(u, v, 1, 0);
    gp_Vec dv = cone->DN(u, v, 0, 1);
    du.Normalize();
    dv.Normalize();

    std::cout << "\nResult of DN\n";
    std::cout << "(" << du.X() << ", " << du.Y() << ", " << du.Z() << ")\n";
    std::cout << "(" << dv.X() << ", " << dv.Y() << ", " << dv.Z() << ")\n";

    gp_Pnt pnt;
    cone->D1(u, v, pnt, du, dv);
    du.Normalize();
    dv.Normalize();

    std::cout << "\nResult of D1\n";
    std::cout << "(" << du.X() << ", " << du.Y() << ", " << du.Z() << ")\n";
    std::cout << "(" << dv.X() << ", " << dv.Y() << ", " << dv.Z() << ")\n";

    GeomLProp_SLProps prop(cone, u, v, 2, Precision::Confusion());
    if (prop.IsTangentVDefined()) {
        gp_Dir du, dv;
        prop.TangentU(du);
        prop.TangentV(dv);
        std::cout << "\nResult of GeomLProp_SLProps\n";
        std::cout << "(" << du.X() << ", " << du.Y() << ", " << du.Z() << ")\n";
        std::cout << "(" << dv.X() << ", " << dv.Y() << ", " << dv.Z() << ")\n";
    }

    du = DN(cone, u, v, 1, 0);
    dv = DN(cone, u, v, 0, 1);
    du.Normalize();
    dv.Normalize();

    std::cout << "\nResult of fixed ElSLib::ConeDN\n";
    std::cout << "(" << du.X() << ", " << du.Y() << ", " << du.Z() << ")\n";
    std::cout << "(" << dv.X() << ", " << dv.Y() << ", " << dv.Z() << ")\n";
}

The error was reported in the FreeCAD forum: https://forum.freecadweb.org/viewtopic.php?f=10&t=66677