Cancelling the Direct ship Order Line did not Reduce the Total Credit Exposure for Customer

I had an Direct ship Order (SD/OD) in Enterprise one 9.1  version. Instead of cancelling the Direct ship Line in the sales order side , user by mistakenly cancelled the Direct ship Purchase order line. It did can cell the Direct ship Purchase Order & also did cancel the Direct ship Sales order line. At the end we notice though it has cancelled the Direct ship Sales side line Successfully , it has not reduced the total Credit Exposure or Total Open order vale for the  Customer .

Is this a BUG ???? How can I fix that ??