Granite SourceList bug

public static void main (string[] args) {
    Gtk.init (ref args);
    var win = new Gtk.Window();
    var box = new Gtk.Box (Gtk.Orientation.HORIZONTAL, 0);
    var root = new Granite.Widgets.SourceList.ExpandableItem ("root");
    var sl = new Granite.Widgets.SourceList (root);
    root.add (new Granite.Widgets.SourceList.Item ("item1"));
    root.add (new Granite.Widgets.SourceList.Item ("item2"));
    root.add (new Granite.Widgets.SourceList.Item ("item3"));
    var item4 = new Granite.Widgets.SourceList.ExpandableItem ("sub");
    var sub1 = new Granite.Widgets.SourceList.Item ("sub1");
    sub1.icon = new ThemedIcon ("media-playback-start");
    var sub2 = new Granite.Widgets.SourceList.Item ("sub2");
    sub2.icon = new ThemedIcon ("media-playback-start");
    var sub3 = new Granite.Widgets.SourceList.Item ("sub3");
    sub3.icon = new ThemedIcon ("media-playback-start");
    item4.add (sub1);
    item4.add (sub2);
    item4.add (sub3);
    root.add (item4);
    box.pack_start (sl, false, false);
    var model = new Gtk.ListStore (1, typeof (int));
    var tree_view = new Gtk.TreeView.with_model (model);
    tree_view.insert_column_with_attributes (-1, "toto", new Gtk.CellRendererText(), "text", 0);
    box.pack_start (tree_view);
    win.add (box);
    win.show_all();
    Gtk.main();
}