Bug#661670: seems to be fixed in upstream

[jasen betts]

https://github.com/bbangert/beaker/blob/master/beaker/session.pydef

def _delete_cookie(self):
self.request['set_cookie'] = True
expires = datetime.utcnow() - timedelta(365)
self._set_cookie_values(expires)
self._update_cookie_out()