PO acceptance notification keep reappearing

We are on 12.1.3 and our POs require acceptance.If these are not accepted then the buyer gets a notification "Standard Purchase Order 16801 has not been accepted by the acceptance due date".The buyer closes  this notification in the notifications summary page(but does not enter the acceptance on the PO).Once this notification is closed manually , the notification reappears after some time for the same PO .Is this normal or should the notification once closed manually not appear again ?

Thanks

Rahul