Error during JPA flush - Encountered unmanaged object in life cycle state unmanaged while cascading persistence

Question

I am using Open JPA 2.4.2 on an OSGI platform with Apache Aries JPA 2.6.1 My DAO is injected using Apache Aries Blueprint.

blueprint.xml

<blueprint default-activation="lazy"
xmlns="http://www.osgi.org/xmlns/blueprint/v1.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:jpa="http://aries.apache.org/xmlns/jpa/v2.0.0" xmlns:tx="http://aries.apache.org/xmlns/transactions/v1.0.0"
xmlns:jaxrs="http://cxf.apache.org/blueprint/jaxrs" xmlns:cxf="http://cxf.apache.org/blueprint/core">

<jpa:enable />

<bean id="appDAO"
class="com.test.MyDAOImpl">
    <tx:transaction method="*" value="Required" />
</bean>
</blueprint>

MyDAOImpl has the EntityManager injected using annotations

public class MyDAOImpl implements MyDAO {

@PersistentContext(unitName = "test-unit")
private EntityManager entityManager;

public EntityObj getEntityObj(int id) {
    return entityManager.find(EntityObj.class, id);
}

public void saveParentObj(ParentOfEntity parentOfEntity) {
    entityManager.persist(parentOfEntity);
    entityManager.flush();
}
}

MyServiceImpl.java

private MyDAO myDAO;

public void updateEntityObj(int id) {
    ParentOfEntity parent = new ParentOfEntity();
    EntityObj obj = myDAO.getEntityObj(id);
    obj.setValue1("1");
    obj.setValue2("2");
    parent.setChild(obj);
    myDAO.saveParentObj(parent);
}

ParentOfEntity.java

class ParentOfEntity {
    private EntityObj child;
    ...
}

This throws an exception

org.apache.openjpa.persistence.InvalidStateException: Encountered unmanaged 
object "com.test.EntityObj-15389840" in life cycle state  unmanaged while 
cascading persistence via field "com.test.ParentOfEntity.child" during 
flush.  However, this field does not allow cascade persist. You cannot flush 
unmanaged objects or graphs that have persistent associations to unmanaged 
objects.
Suggested actions: a) Set the cascade attribute for this field to 
CascadeType.PERSIST or CascadeType.ALL (JPA annotations) or "persist" or 
"all" (JPA orm.xml), 
b) enable cascade-persist globally, 
c) manually persist the related field value prior to flushing. 
d) if the reference belongs to another context, allow reference to it by 
setting StoreContext.setAllowReferenceToSiblingContext().

If I fetch the child - EntityObj again in the saveParentObj method of MyDAO, then it goes through successfully. But this is unnecessary since I already have the entityObj reference and which also has been updated.

Can you advise on any other solution for the same?