Opencascade. AccessViolation when wrapping C++ pointer in C#

Question

I'm trying to use opencascade from C#. I have started from the .NET example with the OCCTProxy. To keep track of the shapes created i use this class, NativeWrapper, to keep a pointer to the objects.

public ref class NativeWrapper
{
  public:
     NativeWrapper();

     // Allocate the native object on the C++ Heap via a constructor
     NativeWrapper(void* topoDs) : m_Impl(topoDs) {}

     // Deallocate the native object on a destructor
     ~NativeWrapper() {
          delete m_Impl;
     }

  protected:
     // Deallocate the native object on the finalizer just in case no destructor is called
     !NativeWrapper() {
          delete m_Impl;
     }

  public:
     void* GetPointer() { return m_Impl; }

  private:
     void* m_Impl;
};

Here the shape is drawn and the NativeWrapper is set as a tag on the treenode

TopoDS_Shape MakeBox(Standard_Real x0, Standard_Real y0, Standard_Real z0, Standard_Real xDelta, Standard_Real yDelta, Standard_Real zDelta)
{
     gp_Pnt center(x0, y0, z0);
     BRepPrimAPI_MakeBox mkBox(center, xDelta, yDelta, zDelta);
     TopoDS_Shape shape = mkBox.Shape();
     return shape;
}

NativeWrapper^ DrawBox(Standard_Real x0, Standard_Real y0, Standard_Real z0, Standard_Real xDelta, Standard_Real yDelta, Standard_Real zDelta)
{
     TopoDS_Shape shape = MakeBox(x0, y0, z0, xDelta, yDelta, zDelta);
     myAISContext()->Display(new AIS_Shape(shape));
     TopoDS_Shape* retVal = new TopoDS_Shape(shape);
     NativeWrapper ^f = gcnew NativeWrapper(retVal);
     return f;
}     

private void ribbonButtonAddBox_Click(object sender, EventArgs e)
{
     var dlg = new DrawCubeDialog();
     dlg.StartPosition = System.Windows.Forms.FormStartPosition.CenterParent;
     if (dlg.ShowDialog() == System.Windows.Forms.DialogResult.OK)
     {
          var data = dlg.CubeData;
          var o = Viewer.DrawCube(data.Name, data.Point, data.XDelta, data.YDelta, data.ZDelta);
          treeNodePrimitives.Nodes.Add(new TreeNode(data.Name) { Tag = o });
     }
}

But when i try to use the object i get this exception

System.AccessViolationException was unhandled Message=Attempted to read or write protected memory. This is often an indication that other memory is corrupt. Source=OCCTProxy StackTrace: at Handle_Standard_Transient.BeginScope(Handle_Standard_Transient* ) at Handle_Standard_Transient.{ctor}(Handle_Standard_Transient* , Handle_Standard_Transient* aTid) in c:\opencascade6.7.0\opencascade-6.7.0\inc\handle_standard_transient.hxx:line 82 at Handle_MMgt_TShared.{ctor}(Handle_MMgt_TShared* , Handle_MMgt_TShared* aHandle) in c:\opencascade6.7.0\opencascade-6.7.0\inc\handle_mmgt_tshared.hxx:line 25 at Handle_TopoDS_TShape.{ctor}(Handle_TopoDS_TShape* , Handle_TopoDS_TShape* aHandle) in c:\opencascade6.7.0\opencascade-6.7.0\inc\handle_topods_tshape.hxx:line 25 at TopoDS_Shape.{ctor}(TopoDS_Shape* , TopoDS_Shape* A_0) ...

NativeWrapper^ Partition(void* objA, void* objB)
{
     TopoDS_Shape* p_A = static_cast<TopoDS_Shape*>(objA);
     TopoDS_Shape* p_B = static_cast<TopoDS_Shape*>(objB);

     TopoDS_Shape a = *p_A;
     TopoDS_Shape b = *p_B;

     BOPAlgo_Builder aBuilder;
     aBuilder.AddArgument(a);
     aBuilder.AddArgument(b);
     aBuilder.Perform();
     Standard_Integer iErr = aBuilder.ErrorStatus();
     if (iErr)
     {
          // TODO: HANDLE ERROR
     }
     const TopoDS_Shape& shape = aBuilder.Shape();
     TopoDS_Shape retVal = shape;

     ClearView();
     Draw(retVal);

     NativeWrapper ^f = gcnew NativeWrapper(&retVal);
     return f;
}

Any one who can explain to me what is going wrong here, and how to do this right?

Any help much appreciated :)