@Entity
public class Boat {
   @Id @GeneratedValue
   private Long id;
   
   @OneToMany( cascade=CascadeType.ALL )
   @Size( min = 1 )
   @NotNull
   private List< Person > crew;

   private boolean sink;
   
   public Long getId() {
      return id;
   }

   public boolean isSink() {
      return sink;
   }

   public void setSink(boolean sink) {
      this.sink = sink;
   }

   public List<Person> getCrew() {
      if( crew == null )
         crew = new ArrayList< Person >();
      
      return crew;
   }

   public void setCrew(List<Person> crew) {
      this.crew = crew;
   }
}

@Entity
public class Person {
   @Id @GeneratedValue
   private Long id;

   @OneToMany( cascade=CascadeType.ALL )
   @Size( min = 1 )
   @NotNull
   private List< Shoe > shoes;

   public List<Shoe> getShoes() {
      if( shoes == null )
         shoes = new ArrayList< Shoe >();
      
      return shoes;
   }

   public void setShoes(List<Shoe> shoes) {
      this.shoes = shoes;
   }

}

@Entity
public class Shoe {
   @Id @GeneratedValue
   private Long id;

}

      EntityManagerFactory emf = Persistence.createEntityManagerFactory( "myDatabase" );

// first transaction, persisting entities
      EntityManager em = emf.createEntityManager();      
      em.getTransaction().begin();      
      Boat b = new Boat();
      Person p = new Person();
      Shoe s = new Shoe();
      p.getShoes().add( s );
      b.getCrew().add( p );      
      em.persist( b );
      em.getTransaction().commit();
      em.close();
      
// second transaction trying to sink the boat
      em = emf.createEntityManager();
      em.getTransaction().begin();
      b = em.find( Boat.class, b.getId() );
      b.setSink( true );
      em.getTransaction().commit();
      em.close();
      emf.close();

SEVERE: an assertion failure occured (this may indicate a bug in Hibernate, but is more likely due to unsafe use of the session)
org.hibernate.AssertionFailure: collection [Person.shoes] was not processed by flush()
   at org.hibernate.engine.CollectionEntry.postFlush(CollectionEntry.java:205)

b.getCrew().get( 0 ).getShoes();