Alias in InnerJoin-Update-Queries wrong

I tried to do an UPDATE-Operation like the following example:

$query = Doctrine_Query::create()
->update('PickingRequestStatus s')
->innerJoin('s.Request r')
->innerJoin('r.WorkStatus ws')
->set('s.status=?', PickingRequestStatus::$STATUS_WORK_CANCELLED)
->where('s.status = ?', array(PickingRequestStatus::$STATUS_WORK_STARTED))
->andWhere('ws.last_action_at < ?', $threshold);

The created SQL-Statement is wrong:
UPDATE sd_picking_request_status INNER JOIN sd_picking_request s2 ON s.request_id = s2.id INNER JOIN sd_picking_request_work_status s3 ON s2.id = s3.request_id SET status = 16 WHERE status = 8 AND last_action_at < '2009-11-08 11:00'

and you will get the following error-message: SQLSTATE[42S22]: Column not found: 1054 Unknown column 's.request_id' in 'on clause'

If you remove the s. in the JOIN-Statement everthing is fine:

UPDATE sd_picking_request_status INNER JOIN sd_picking_request s2 ON request_id = s2.id INNER JOIN sd_picking_request_work_status s3 ON s2.id = s3.request_id SET status = 16 WHERE status = 8 AND last_action_at < '2009-11-09 11:00'