JPQL-UPDATE + refresh() sets collections to NULL

[Sebastian Gauder]

I have the following piece of Code:

static ConcurrentLinkedQueue<Band> bands;
...
public int perform(EntityManager em) {
   Band b = em.merge(bands.poll());
        try {
           String statement = "UPDATE Band AS b " +
                   "SET b.name='The "+b.getName()+"'"+
                   " WHERE b.id="+b.getId();
           Query query = em.createQuery(statement);
           query.executeUpdate();
          
           statement = "UPDATE Album AS a " +
           "SET a.name='The "+b.getName()+"'"+
           " WHERE a.id="+b.getAlbums().get(0).getId();
           query = em.createQuery(statement);
           query.executeUpdate();
          
           if (b.getTour()!=null) {
               statement = "UPDATE Concert AS c " +
               "SET c.city='London' "+
               "WHERE c.id="+b.getTour().getConcerts().get(0).getId();
               query = em.createQuery(statement);
               query.executeUpdate();
           }
          
           em.refresh(b);
           bands.add(b);
          
           return 0;
       }
       catch (Exception e) {
           e.printStackTrace();
           return -1;
       }
   }


The Entity Band looks like this:

@Entity
@Table(name="JBT_Band")
public class Band {

   private Long id;

   @Id
   @GeneratedValue
   public Long getId() {
       return id;
   }

   public void setId(Long id) {
       this.id = id;
   }
  
   private String name;
  
   public String getName() {
       return name;
   }

   public void setName(String name) {
       this.name = name;
   }

  
   private List<Artist> members;

   @OneToMany(cascade=ALL, mappedBy = "band")
   public List<Artist> getMembers() {
       return members;
   }

   public void setMembers(List<Artist> members) {
       this.members = members;
   }
  
   private Tour tour;

   @OneToOne(cascade=ALL, optional = true, mappedBy = "band")
   public Tour getTour() {
       return tour;
   }

   public void setTour(Tour tour) {
       this.tour = tour;
   }
  
   private List<Album> albums;

   @OneToMany(cascade=ALL, mappedBy = "band")
   public List<Album> getAlbums() {
       return albums;
   }

   public void setAlbums(List<Album> albums) {
       this.albums = albums;
   }
  
   private int scenario;

   public int getScenario() {
       return scenario;
   }

   public void setScenario(int scenario) {
       this.scenario = scenario;
   }
  
}

The method perform() is processed by up to 10 Threads at the same time. 
Each thread retrieves an entity 'Band' from a static and threadsafe 
queue and updates the according table and some related tables by 
JPQL-Queries.
The problem is, that after refresh() the lists 'albums' and 'members' 
are set to NULL which causes NullPointerExceptions in other places. Is 
this a bug in OpenJPA? (Code works in Hibernate and TopLink)

Regards,
Seb