net.sf.hibernate.HibernateException: Found two representations of same collection

[真不知道是谁]

[java] net.sf.hibernate.HibernateException: Found two representations of same collection: com.boco.hibernate.Province.citys
[java] at net.sf.hibernate.impl.SessionImpl.updateReachableCollection(SessionImpl.java:2890)
[java] at net.sf.hibernate.impl.FlushVisitor.processCollection(FlushVisitor.java:32)
[java] at net.sf.hibernate.impl.AbstractVisitor.processValue(AbstractVisitor.java:69)
[java] at net.sf.hibernate.impl.AbstractVisitor.processValues(AbstractVisitor.java:36)
[java] at net.sf.hibernate.impl.SessionImpl.flushEntity(SessionImpl.java:2612)
[java] at net.sf.hibernate.impl.SessionImpl.flushEntities(SessionImpl.java:2478)
[java] at net.sf.hibernate.impl.SessionImpl.flushEverything(SessionImpl.java:2280)
[java] at net.sf.hibernate.impl.SessionImpl.flush(SessionImpl.java:2259)
[java] at net.sf.hibernate.transaction.JDBCTransaction.commit(JDBCTransaction.java:61)
[java] at com.boco.hibernate.TestHibernateService.insertProv(TestHibernateService.java:140)
[java] at com.boco.hibernate.TestHibernateService.main(TestHibernateService.java:297)
[java] function total:24805 query: 0 result: 24805
BUILD SUCCESSFUL
Total time: 51 seconds


Found two representations of same collection
这个问题好象不是很普遍。大家见过吗？
这是怎么回事呀。我的是4个表关联。