passing -1 to gtk_combo_box_set_active behaves different than docs state

[Christian Neumair <chris gnome-de org>]

I've attached a sample that demonstrates that gtk_combo_box_set_active
selects the last item in the ComboBox if -1 is passed. [1] states that
-1 tells the ComboBox to have no active item at all. Is there any way to
select nothing at all (empty ComboBox, user can select an entry)?
I can verify this problem with custom cell renderers as well.


[1]
http://developer.gnome.org/doc/API/2.2/gtk/GtkComboBox.html#gtk-combo-box-set-active

all:
	gcc `pkg-config --cflags --libs gtk+-2.0 glib-2.0` testcombo.c -o testcombo

#include <gtk/gtk.h>

const char* menu_entries [] = {
	"foo",
	"test!",
	"last one..."
};

static void
button_clicked_cb (G_GNUC_UNUSED GtkButton *button, GtkComboBox *combo) {
	g_warning ("trying to set active combobox item to -1");

	gtk_combo_box_set_active (combo, -1);
}

int
main (int argc, char **argv) {
	GtkWidget *window, *vbox, *combo, *button;
	guint i;

	gtk_init (&argc, &argv);

	window = gtk_window_new (GTK_WINDOW_TOPLEVEL);

	vbox = gtk_vbox_new (FALSE, 6);
	gtk_container_add (GTK_CONTAINER (window), vbox);

	/* create the combobox */
	combo = gtk_combo_box_new_text ();
	for (i = 0; i < G_N_ELEMENTS (menu_entries); i++) {
		gtk_combo_box_append_text (GTK_COMBO_BOX (combo),
					   menu_entries[i]);
	}
	gtk_combo_box_set_active (GTK_COMBO_BOX (combo), 0);
	gtk_container_add (GTK_CONTAINER (vbox), combo);

	button = gtk_button_new_with_label ("set active combobox item to -1");
	g_signal_connect (G_OBJECT (button),
			  "clicked", G_CALLBACK (button_clicked_cb),
			  G_OBJECT (combo));
	gtk_container_add (GTK_CONTAINER (vbox), button);
	
	gtk_widget_show_all (window);

	gtk_main ();

	return 0;
}