Active Query bug?

Check rest of your queries - this very well may be when you have done $this->db->select('id') somewhere else, but not executed query with $this->db->get(...);

You could try adding $this->db->reset_query() right before your $this->db->select('s_cities.id as source_city_id, d_cities.id as destination_city_id, jobs_raw.*') to make sure.