should all-delete-orphan work for both unidirectional and bidirectional (one2many association) ? is there any rule for this ..

I am trying to delete a child element using all-delete-orphan.... but getting following exception.. .


INFO: Checking 0 named queries
Hibernate: select dept0_.id as id0_, dept0_.name as name1_0_ from dept dept0_ where dept0_.id=?
Hibernate: select emp0_.deptid as deptid__, emp0_.id as id__, emp0_.id as id0_, emp0_.name as name0_0_, emp0_.deptid as deptid0_0_ from emp emp0_ where emp0_.deptid=?
Exception in thread "main" java.util.ConcurrentModificationException
at java.util.HashMap$HashIterator.nextEntry(Unknown Source)
at java.util.HashMap$KeyIterator.next(Unknown Source)
at org.hibernate.collection.AbstractPersistentCollection$IteratorProxy.next(AbstractPersistentCollection.java:357)
at Test.removeUser(Test.java:55)
at Test.main(Test.java:66)

Below is my code :

<hibernate-mapping>
<class name="Employee" table="emp">
<id name="empId" column="id">
<generator class="native"/>
</id>
<property name="empName" column="name"/>
<many-to-one name="deptid" column="deptid"/>
</class>
</hibernate-mapping>

<hibernate-mapping>
<class name="Dept" table="dept">
<id name="deptId" column="id">
<generator class="native"/>
</id>
<property name="deptName" column="name"/>

<set name="emp" cascade="all-delete-orphan">
<key column="deptid"/>
<one-to-many class="Employee"/>
</set>

</class>
</hibernate-mapping>

Session session = sessionFactory.openSession();
Transaction tx = session.beginTransaction();
Dept dept=(Dept)session.load(Dept.class,new Integer(1));
Iterator<Employee> emps=((Set)dept.getEmp()).iterator();
while(emps.hasNext()){
Employee emp=emps.next();
if(emp.getEmpName().equals("user")){
dept.getEmp().remove(emp);
}
}
tx.commit();
session.close();