TreeFilterModel and sorting

[bernd <Bernd Demian csc-dd de>]

Hi,
we use GtkTreeModelFilter to filter a modell to diff. views. Ok it
works. But we can't sorting the view because the model in dthe view is
not a SORTABLE. 
In function:
gboolean
gtk_tree_sortable_get_sort_column_id (GtkTreeSortable  *sortable,
				      gint             *sort_column_id,
				      GtkSortType      *order)
{
  GtkTreeSortableIface *iface;

  g_return_val_if_fail (GTK_IS_TREE_SORTABLE (sortable), FALSE);

from gtk_tree_column_sort:

  has_sort_column =
    gtk_tree_sortable_get_sort_column_id (GTK_TREE_SORTABLE
(GTK_TREE_VIEW (tree_column->tree_view)->priv->model),
					  &sort_column_id,
					  &order);

we get the error message:
Gtk-CRITICAL **: file gtktreesortable.c: line 108
(gtk_tree_sortable_get_sort_column_id): assertion `GTK_IS_TREE_SORTABLE
(sortable)' failed

Is it not possible to sort a view with FilterModel?
Or have me make a failure in bilding the view?

MfG Bernd