Is it right in ERP to cancel Sales Order after return from Customer?

Following is the scenario where I want to handle return processing. In my case cancelling Delivery order is not in option, otherwise I would have cancelled Delivery Order and Sale Order.

1). Customer places order through the different channels. Order is confirmed in OpenER and devliery order gets created.

2). The Delivery order is dispatched from warehouse through courier and it's marked as done. 

3). In some scenarios, the parcel is returned from Customer. We create Return(Incoming Shipment) against delivered delivery order.

4). When we try to cancel Sale Order it says "'Cannot cancel sales order!', u'You must first cancel all delivery order(s) attached to this sales order.'" But I can't cancel Delivery order because the delivery order was gone through two processes(delivery and return).

My question, Is it right to cancel Sales Order which is returned from Customer. Or we can keep return order in "Sales Order or Sale to Invoice" state.?

Previously Asked Question : 

https://www.odoo.com/forum/help-1/question/openerp-7-cancel-sales-order-38271