diff --git a/addons/purchase/purchase.py b/addons/purchase/purchase.py
index cc300516dd0..8f58dc32c10 100644
--- a/addons/purchase/purchase.py
+++ b/addons/purchase/purchase.py
@@ -300,6 +300,8 @@ class purchase_order(osv.osv):
         self.write(cr, uid, ids, {'state':'draft','shipped':0})
         wf_service = netsvc.LocalService("workflow")
         for p_id in ids:
+            # Deleting the existing instance of workflow for PO
+            wf_service.trg_delete(uid, 'purchase.order', p_id, cr)            
             wf_service.trg_create(uid, 'purchase.order', p_id, cr)
         return True
 
diff --git a/addons/sale/sale.py b/addons/sale/sale.py
index 36cd10a4311..263c5f3c233 100644
--- a/addons/sale/sale.py
+++ b/addons/sale/sale.py
@@ -303,6 +303,8 @@ class sale_order(osv.osv):
         self.pool.get('sale.order.line').write(cr, uid, line_ids, {'invoiced': False, 'state': 'draft', 'invoice_lines': [(6, 0, [])]})
         wf_service = netsvc.LocalService("workflow")
         for inv_id in ids:
+            # Deleting the existing instance of workflow for SO
+            wf_service.trg_delete(uid, 'sale.order', inv_id, cr)
             wf_service.trg_create(uid, 'sale.order', inv_id, cr)
         return True