Quantity is get added instead of Subtraction when we create the debit memo

Hi Friends,

I had created a sales order of quantity 25, and then create the partial delivery and invoice of 24 . When I create the debit memo req w.r.t to the sales order it is also getting created for quantity 24.

Now I have created the delivery & invoice of remaining quantity (i.e. Qty = 1).

When I create the debit memo req w.r.t to sales order it is showing me the quantity as 49.

(i.e. 25 + 24 ) instead of subtracting the quantity is getting added .

Please advice.