Many-To-Many relationship not working in Hibernate

[Ashok Pradhan]

My entity Classes

Teacher

@Entity
public class Teacher implements Serializable {

	private static final long serialVersionUID = -225072121828354819L;
	@Id
	@GeneratedValue
	@Column(name = "TEACH_ID")
	private Long id;
	private String name;
	@ManyToMany(cascade = CascadeType.ALL)
	@JoinTable(name = "TEACHER_SECTION", joinColumns = { @JoinColumn(name = "TEACH_ID") },
										inverseJoinColumns = { @JoinColumn(name = "SEC_ID") })
       private Set<Section> sections = new HashSet<Section>();
//Getters and Setters hashCode and toString

Section

@Entity
public class Section implements Serializable{


	private static final long serialVersionUID = 4048263688849778627L;
	@Id
	@GeneratedValue
	@Column(name="SEC_ID")
	private Long id;
	private String name;
	@ManyToMany(mappedBy="sections",targetEntity=com.association.entity.Teacher.class)
	private Set<Teacher> teachers = new HashSet<Teacher>();

       //Getters ,Setters ,hashCode and toString

Main Class

Session session = AppHibernateSessionFactory.getSession();
		Transaction tx = session.beginTransaction();
		
		Teacher teacher = new Teacher();
		Section section1 = new Section();
		Section section2 = new Section();
		
		teacher.setName("Ashok");
		section1.setName("A");
		section2.setName("B");
		
		//session.save(section1);                     //Line 1
		//session.save(section2);                     //Line 2
		
		teacher.getSections().add(section1);
		teacher.getSections().add(section2);
		
		session.save(teacher);
		
		tx.commit();
		session.close();
		AppHibernateSessionFactory.getSessionFactory().close();

Everything works well if I include

session.save(section1);
session.save(section2);

before I call

session.save(teacher);

Otherwise the generated JoinTable and Section table does not include section2 data
But my question is - As I have annotated

@ManyToMany(cascade = CascadeType.ALL)

in Teacher class the above things (saving section objects before teacher object) are not necessary.

Please show me some light ...