问为什么在下面的示例中从集合中移除实体的操作不会被传播？

EN

@Entity
public class C {

  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  private int id;
  ...
  @ManyToOne(fetch = FetchType.EAGER, cascade = {CascadeType.PERSIST, CascadeType.MERGE})
  @JoinColumn(name="B_ID")
  private B b;
  ...
}

@Entity
public class B {

  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  private int id;
  private String name;

  @OneToMany(mappedBy = "b", fetch = FetchType.EAGER, cascade = {CascadeType.REMOVE, CascadeType.MERGE})
  private Set<C> cs;

  @ManyToOne(fetch = FetchType.EAGER, cascade = {CascadeType.PERSIST, CascadeType.MERGE})
  @JoinColumn(name = "A_ID")
  private A a;
  ...
}

@Entity
public class A {
  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  private int id;

  @OneToMany(mappedBy = "tenant", fetch = FetchType.EAGER, cascade ={CascadeType.PERSIST, CascadeType.MERGE, CascadeType.REMOVE})
  private Set<B> bs;
  ...
}

@Stateless
public class BServiceBean implements BService {

  @PersistenceContext(unitName = Constants.PU)
  EntityManager em;

  @Override
  public B updateB(B b) {
    return em.merge(b);
  }

  @Override
  public B removeC(int bId, int cId) throws IllegalArgumentException {
    B b = em.find(B.class, bId);

    if (null == b) {
      throw new IllegalArgumentException("No b with id: " + bId + " exists.");
    }
    C c = em.find(C.class, cId);

    if (null == c) {
      throw new IllegalArgumentException("No c with id: " + cId + " exists.");
    }
    b.getCs().remove(c);
    em.remove(c);
    return em.merge(b);
  }
}

// created and persisted an A with three Bs, one of which has three Cs. 
A a = ...;
b2.setName(changedName);
b2 = bService.updateB(b2); // this change is reflected in a
...
b2 = bService.removeC(b2.getId(), c1.getId()); // this change is not reflected in a

// but it is in the db
a = aService.findAById(a.getId); // this instance of a has a b2 without a c1