Hibernate: Where do insertable = false, updatable = false belong in composite primary key constellations involving foreign keys?

When implementing composite primary keys in Hibernate or other ORMs there are up to three places where to put the insertable = false, updatable = false in composite primary key constellations that use identifying relationships (FKs that are part of the PK):

1. Into the composite PK class' @Column annotation (@Embeddable classes only) or
2. Into the entity class' association @JoinColumn/s annotation or
3. Into the entity class' redundant PK property's @Column annotation (@IdClass classes only)

The third is the only way to do with @IdClass and JPA 1.0 AFAIK. See http://en.wikibooks.org/wiki/Java_Persistence/Identity_and_Sequencing#Primary_Keys_through_OneToOne_Relationships. I will consider only cases 1. and 2.

Q: Which way is the preferred place to put the "insertable = false, updatable = false" to generally?

I have experienced problems with Hibernate concerning this question. For example, Hibernate 3.5.x will complain about the Zips table

CREATE TABLE Zips
(
  country_code CHAR(2),
  code VARCHAR(10),
  PRIMARY KEY (country_code, code),
  FOREIGN KEY (country_code) REFERENCES Countries (iso_code)
)

with:

org.hibernate.MappingException: Repeated column in mapping for entity: com.kawoolutions.bbstats.model.Zip column: country_code (should be mapped with insert="false" update="false")
org.hibernate.mapping.PersistentClass.checkColumnDuplication(PersistentClass.java:676)
org.hibernate.mapping.PersistentClass.checkPropertyColumnDuplication(PersistentClass.java:698)
...

As you can see the country_code column is both PK and FK. Here are its classes:

Entity class:

@Entity
@Table(name = "Zips")
public class Zip implements Serializable
{
    @EmbeddedId
    private ZipId id;

    @ManyToOne
    @JoinColumn(name = "country_code", referencedColumnName = "iso_code")
    private Country country = null;
...
}

Composite PK class:

@Embeddable
public class ZipId implements Serializable
{
    @Column(name = "country_code", insertable = false, updatable = false)
    private String countryCode;

    @Column(name = "code")
    private String code;
...
}

When putting the insertable = false, updatable = false into the entity class association's @JoinColumn all exceptions disappear and everything work fine. However, I don't see why the above code should not be working. It might be Hibernate having problems with this. Is the described a Hibernate bug, as it doesn't seem to evaluate @Column "insertable = false, updatable = false"?

In essence, what's the standard JPA way, the best practice, or preference where to put "insertable = false, updatable = false"?