ALE (SALES ORDER)

hi every body,

i was stuck in a serious problem,please help me out.i configured an ALE scenario where PO in one system will Creates a SO in other.now for example a salesorder is created with refernce to PO number 12345(trough ale).here if we create a Standard Sales order with refer to same PO 12345.it is accepting.it means these are duplicate Sales orders.how to come over this problem,please help me out.