JPA manytomany unidirectional mapping update problem

I have two class Group and Permission ,Group has a list of Permission when i try do add new permission to a group.I set new List of permission and commit successfully but no update occur at database.I am using jpa 1 (hibernate as provider).I am creating request per entitymanager (not jta) .My managed bean request scope (a4j:keepalive) and I try this for locate erro but not successfull.

1-Getting current group for editing as Select g from Group g join fetch g.permissions where g.id= :id if it result from Lazy fetch of permission list(as here)

2-Refreshing all permission in list from database then merge group.

public class GroupEditorBean extends AbstractGroupBean {
    private static final long serialVersionUID = -7454051588934099916L;



    @PostConstruct
    public void init() {
        this.group=  groupAccessor.findGroup(Long.valueOf(getParameter("group")));
        perms =  this.group.getPermIdList();
    }


    public String save() {
        if(group.isRoot()){
            addError("Root  group can not be updated");
            return "";
        }
       List<Permission> permissions=   convertToPermission(perms);
        this.group.setPermissions(permissions);
        groupAccessor.merge(group);
        logger.log(String.format("Updated group %s", group.getName()), "group",
                Log.Severity.INFO);

        return "modules/user/groups.xhtml";
    }







@Entity
@Table(name = "GROUPS")
public class Group implements Serializable {
    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "GID")
    private Long id;



    @ManyToMany(cascade={CascadeType.MERGE,CascadeType.PERSIST,CascadeType.REFRESH})
    @JoinTable(name = "GROUP_PERMISSION", joinColumns = @JoinColumn(name = "GID"), inverseJoinColumns = @JoinColumn(name = "PID"))
    private List<Permission> permissions;





@Entity
@Table(name = "PERMISSIONS")
public class Permission implements Serializable {
    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "PID")
    private Long id;

    @NotNull
    @Column(name = "READA开发者_如何学GoBLE_ID", unique = true)
    private String readableId;

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JPA 1 has problem with orphan entities and JPA-1 implementation jar of hibernate have some extra bugs. Setting list to null solve my problem for this case .I hope JPA-2 solves this problems.