why on_configure_event() is never called here ?

[Renato Merli <merli renato gmail com>]

class myCtn : public Gtk::Fixed
{

    public:
        Gtk::Button btn;
        int x, y;

     bool on_configure_event (GdkEventConfigure *e)
    {
        printf("\non configure");
        return false;

    };


        void botao_clicked()
    {
        x += 25;
        y = x;
        Gtk::Button *tmp = new Gtk::Button("Button");
        put(*tmp, x, y);
        tmp->show();
    };



        myCtn(): btn("Botao"){
            add_events (Gdk::ALL_EVENTS_MASK);
            put (btn,0,0);
            btn.signal_clicked().connect(sigc::mem_fun(this,
&myCtn::botao_clicked));
            x=y=0;
            btn.show();

        };




};



int main (int argc, char *argv[])
{

    Gtk::Main kit(argc, argv);
    Gtk::Window win;

    myCtn box;
    win.add(box);
    win.show_all();
    Gtk::Main::run(win);

}


What am i missing ?
Thank's in advance.