purchase order

dear all,

i have a scenario that we have created a PO and done the goods receipt at the receiving plant,thru MIGO, per se , today's date.(24/07/2008)

now i want to return few material from that PO . we have done return delivery w r t material doc.no.for date of a previous month ( 12/06/2008)

doc got posted . I have not found any logic in this !!!

Kindly explain how return delevery could happen and get posted for a date of previous month when material itself hasn't arrived at receiving plant.

thanks

shankar