@OrderColumn, @OneToMany & null index column for collection

I am trying to create parent child tables where the order is preserved. The example 7.8 from Hibernate documentation shows how to do this:

@Entity
public class Customer {
   @Id @GeneratedValue public Integer getId() { return id; }
   public void setId(Integer id) { this.id = id; }
   private Integer id;

   @OneToMany(mappedBy="customer")
   @OrderColumn(name="orders_index")
   public List<Order> getOrders() { return orders; }
   public void setOrders(List<Order> orders) { this.orders = orders; }
   private List<Order> orders;
}

@Entity
public class Order {
   @Id @GeneratedValue public Integer getId() { return id; }
   public void setId(Integer id) { this.id = id; }
   private Integer id;

   public String getNumber() { return number; }
   public void setNumber(String number) { this.number = number; }
   private String number;

   @ManyToOne
   public Customer getCustomer() { return customer; }
   public void setCustomer(Customer customer) { this.customer = customer; }
   private Customer number;
}

from http://docs.jboss.org/hibernate/core/3.6/reference/en-US/html/collections.html#collections-indexed

When I try this I get an error: null index column for collections

There is Hibernate issue that describes the problem and gives an invalid example, but it specifically says that the example I gave above from the docs IS valid.

@Entity
public class Parent {
    @OneToMany(mappedBy="parent")
    @OrderColumn(name="order")
    private List<Child> children;
}

@Entity
public class Child {
    @ManyToOne
    private Parent parent;
}

from: https://hibernate.onjira.com/browse/HHH-5390

Maybe I'm being dense, but I don't see the difference between these two examples. One is:

@OneToMany(mappedBy="customer")
@OrderColumn(name="orders_index")

The other is:

@OneToMany(mappedBy="parent")
@OrderColumn(name="order")

And of course, I haven't figured out how to the get OrderColumn to work. Does anyone have any insight into why one of these examples is valid and the other is not?