I don't understand this message

[Andrew V. Shuvalov]

I got the error using gtk--:

/usr/local/include/gtk--.h:900: sorry, not
implemented: adjusting pointers for covariant
returns

What is this?  The code is:

class Gtk_Data : public Gtk_Object {
public:

  static void cpp_class_init(GtkObject*o);
  Gtk_Data(GtkData *castitem);
  static bool isGtkData(Gtk_Object *checkcast);
  Signal_proxy0<void,Gtk_Data> disconnect;
protected:
  virtual void disconnect_impl();
public:
  static void disconnect_callback(GtkData *o);


  typedef GtkData BaseObjectType;
  static Gtk_Class_Proxy_Data c_class;
  virtual c_signals_Data
*internal_getsignalbase();
  static void cpp_class_init(GtkDataClass
*o,c_signals_Data *s) {
    Gtk_Object::cpp_class_init((GtkObjectClass
*)o,s);
    s->disconnect=o->disconnect;
    o->disconnect=disconnect_callback;
  }

private:
  Gtk_Data(void);
};