@Entity
public class MyEntity {

   @Id
   @GeneratedValue
   private Integer id;

   @Temporal(TemporalType.TIMESTAMP)
   private Date created = new Date();

   public Integer getId() {
      return id;
   }
   
   @Override
   public String toString() {
      return "MyEntity [getId()=" + getId() + ", getCreated()=" + getCreated();
   }
  
   public Date getCreated() {
      // no defensive copy here - return straight reference
      return created;
   } 

   public void setCreated(Date created) {
      this.created = created;
   }
}

@Stateless
public class MyService {

   @PersistenceContext
   EntityManager em;

   @TransactionAttribute(TransactionAttributeType.REQUIRES_NEW)
   public Integer persistObject() {
      MyEntity entity = new MyEntity();
      em.persist(entity);

      System.out.println("[persistObject()]" + entity);

      return entity.getId();
   }

   @TransactionAttribute(TransactionAttributeType.REQUIRES_NEW)
   public MyEntity readObject(Integer id) {
      MyEntity entity = em.find(MyEntity.class, id);

      System.out.println("[readObject()]" + entity);

      return entity;
   }

   @TransactionAttribute(TransactionAttributeType.REQUIRES_NEW)
   public Integer modifyObject(Integer id) {
      MyEntity entity = em.find(MyEntity.class, id);

      // Try to change date state without changing its reference.
      entity.getCreated().setTime(0L);
      
      // And now try use regular setter to set new date
      Date d = new Date(0L);
      entity.setCreated(d);

      // Pre-update state is correct - Date is 01.01.1970
      System.out.println("[modifyObject()]" + entity);

      return entity.getId();
   }

}

Integer id = service.persistObject();
// Date is reflecting 'now' - correct
MyEntity entity = service.readObject(id);

// Pre-update state is correct - 01.01.1970
id = service.modifyObject(id);

// Post-update state is incorrect - back to 'now' instead of 01.01.1970
service.readObject(id);