Hibernate: маппинг many-to-many работает только в одну сторону

@Entity
@Table
public class Bus implements Serializable {
 
    @Id
    @Column
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long id;
 
    @Column
    private String model;
 
    @Column
    private int seatsAmount;
 
    @ManyToOne
    private Route route;
 
    @ManyToMany(mappedBy= "buses")
    private Collection<Driver> drivers;

@Entity
@Table
public class Driver implements Serializable {
 
    @Id
    @Column
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long id;
 
    @Column
    private String firstName;
 
    @Column
    private String lastName;
 
[B]    @ManyToMany
    @JoinTable(name="Bus_Driver",
        joinColumns=@JoinColumn(name="driver_id"),
        inverseJoinColumns=@JoinColumn(name="bus_id"))
    private Collection<Bus> buses;[/B]

public class BusDao {
 
    public Long add(Bus bus) {
        Session sess = PersistenceUtil.getSessionFactory().openSession();
        sess.beginTransaction();
        Long result = (Long) sess.save(bus);
        sess.getTransaction().commit();
 
        return result;
    }
 
}

public class DriverDao {
 
    public Long add(Driver driver) {
        Session sess = PersistenceUtil.getSessionFactory().openSession();
        sess.beginTransaction();
        Long result = (Long) sess.save(driver);
        sess.getTransaction().commit();
 
        return result;
    }
    
}