defaultview and (sort-)handler

Hello
Since my question was not answered as a forum topic I like to open a support request:

I fiddled around some while to set up a default view (modified an export from views and put the code in some module). Everything seems to work but the sorthandler. The fields in the sort array are recognized since I can confirm that e.g. changing 'sortoder' form DESC to ASC effects the output.
But it looks that the handler is not called by the view.

  $view->sort = array (
      array (
          'tablename' => 'biblio',
          'field' => 'biblio_year',
          'name' => 'Jahr',
          'help' => 'Erscheinungsjahr',
          'handler' =>  'bgv_uheimat_sort_jahr',
          'sortorder' =>  'DESC',
      ),
      array (
          'tablename' => 'biblio',
          'field' => 'biblio_number',
          'name' => 'nr',
          'help' => 'Heft-Nr.',
          'handler' =>  'bgv_uheimat_sort_heft',
          'sortorder' =>  'ASC',
      ),
  );

And the handler looks like

  function bgv_uheimat_sort_jahr ($op, &$query, $sortinfo, $sort) {
        watchdog('bgv',t('in bgv_uheimat_sort_jahr', array()));
      $query->add_orderby('biblio', 'biblio_year', 'DESC', 'biblio_biblio_year');
  }

Currently installed is views-5.x-1.6.

What do I have to change to get the handler working.
Regards