diff --git a/addons/purchase/purchase.py b/addons/purchase/purchase.py
index 63131ec104d..cbeb2325124 100644
--- a/addons/purchase/purchase.py
+++ b/addons/purchase/purchase.py
@@ -653,6 +653,14 @@ class purchase_order(osv.osv):
             return False
         self.write(cr, uid, ids, {'state':'draft','shipped':0})
         self.set_order_line_status(cr, uid, ids, 'draft', context=context)
+        for po in self.browse(cr, SUPERUSER_ID, ids, context=context):
+            for picking in po.picking_ids:
+                picking.move_lines.write({'purchase_line_id': False})
+            for invoice in po.invoice_ids:
+                po.write({'invoice_ids': [(3, invoice.id, _)]})
+            for po_line in po.order_line:
+                for invoice_line in po_line.invoice_lines:
+                    po_line.write({'invoice_lines': [(3, invoice_line.id, _)]})
         for p_id in ids:
             # Deleting the existing instance of workflow for PO
             self.delete_workflow(cr, uid, [p_id]) # TODO is it necessary to interleave the calls?