Duplicates in OneToMany annotated List

I'm working on a Java project using JPA 2 + Hibernate 4.2.6 and I'm getting a strange behaviour.

In my model I have two related entites: Question and Answer

@Entity
public class Question {
    // ...

    @OneToMany(mappedBy = "question", cascade = CascadeType.ALL, fetch = FetchType.EAGER)
    private Set<Answer> answers;

    // ...
}


@Entity
public class Answer {
    // ...

    @ManyToOne(optional = false)
    @JoinColumn(name = "question_id", nullable = false)
    private Question question;

    // ...
}

This works perfectly: all Answers related to a certain Question are loaded correctly.

But now I need to change the tipe of answers collecton from Set to List. I changed the type and ran the application again and now I get several duplicates in answers... Why is it possible? I know that List allows duplicates, but there are no duplicate records in my DB, so why I get these?

I read about some similar bugs in previous version of Hibernate, but I expect they are solved in last version... am I wrong?

NOTE I need to change Set into List because I need to keep information about the order for answers and, possibly, to change this order.