Gtk TreeView emits a beep

[raum no-log org]

Hello,

I'm programming a tool using Vala langage. I need to manipulate a
treeview, delete an item for example.

I'm trapped the "release key" event but for certain keys, treeview emits a
beep (left or right arrow, del keys).

How can I remove this "beep" ?

################ CODE sample.vala ############
public class Application : Gtk.Window {
        public Application () {
                // Prepare Gtk.Window:
                this.title = "My Gtk.TreeView";
                this.window_position = Gtk.WindowPosition.CENTER;
                this.destroy.connect (Gtk.main_quit);
                this.set_default_size (350, 70);

                // The Model:
                Gtk.ListStore list_store = new Gtk.ListStore (2, typeof (string));
                Gtk.TreeIter iter;

                list_store.append (out iter);
                list_store.set (iter, 0, "Burgenland");
                list_store.append (out iter);
                list_store.set (iter, 0, "Carinthia");
                list_store.append (out iter);
                list_store.set (iter, 0, "Lower Austria");
                list_store.append (out iter);
                list_store.set (iter, 0, "Upper Austria");

                // The View:
                Gtk.TreeView view = new Gtk.TreeView.with_model (list_store);
                this.add (view);

                Gtk.CellRendererText cell = new Gtk.CellRendererText ();
                view.insert_column_with_attributes (-1, "State", cell, "text", 0);

                view.add_events(Gdk.EventMask.KEY_RELEASE_MASK);
                view.key_release_event.connect(on_key_press);
        }

        public  bool on_key_press (Gdk.EventKey event) {
                stdout.printf ("keyval: %lu  hk: %lu\n", event.keyval,
event.hardware_keycode);
                return true;
        }

        public static int main (string[] args) {
                Gtk.init (ref args);

                Application app = new Application ();
                app.show_all ();
                Gtk.main ();
                return 0;
        }
}


####### Compilation ##################
$ valac --pkg gtk+-3.0 sample.vala

Thanks

Regards

Raum