<class name="Person" table="tperson">
<id name="id" column="personpk">
<generator class="native"/>
</id>
<set name="addresses"
table="personaddress">
<key column="personid"/>
<many-to-many column="addressid"
unique="true"
class="Address"/>
</set>
</class>

<class name="Address" table="taddress">
<id name="id" column="addresspk">
<generator class="native"/>
</id>
<join table="personaddress"
inverse="true"
optional="true">
<key column="addressid"/>
<many-to-one name="person"
column="personid"
not-null="true"/>
</join>
</class>

public class Address {
  private Long id;
  private Person person;
  public Address() {}
  public Address(Long id) {
    this.id = id;
  }
  public void setPerson(Person person) {
    this.person = person;
  }
}
public class Person {
  private Long id;
  private Collection<Address> addresses;
  public Person() {}
  public Person(Long id) {
    this.id = id;
  }
  public void addAddress(Address address) {
    if (addresses == null) {
      addresses = new HashSet<Address>();
    }
    addresses.add(address);
  }
}

//create conditions
Transaction transaction = session.session.beginTransaction();
Person person = new Person(idPers);
Address address = new Address(idAddr);
address.setPerson(person);
person.addAddress(address);
session.save(person);
session.save(address);
transaction.commit();
session.clear();

//Now, reproduction of problem
session.beginTransaction();

//this call is necessary for reproduction of problem
session.get(Address.class, idAddr);

Person reloadedPerson = (Person) session.get(Person.class, idPers);
session.delete(reloadPerson);

//Here the exception
Person expectedNullPerson= (Person) session.get(Person.class, idPers);