Sorting a TreeModel

["Joe Van Dyk" <joevandyk gmail com>]

Hi,

I have a TreeModel that's wrapped with a TreeModelSort object.  I then
mark the TreeViewColumn sortable with:
 column->set_sort_column(columns.the_column);

So, when I click on the treeview's column header, it does do the right
thing.  It shows a down arrow and sorts the column ascending.  If I
click the column header again, it shows an up arrow and sorts the
column descending.

However!  If I click the column header again, there's no arrow and the
column goes back to being unsorted.  I don't want this behavior.  The
column should always be sorted one way or another when I click the
column header.

I'm using Gtk and Gtkmm 2.4 if it matters.

Any ideas?

Thanks,
Joe