Delivery is getting created for greater quantity than unrestricted stock

Hi Experts,

How can delivery is getting created for more qty than what is there in unrestricted stock? In MMBE report I found a case where unrestricted qty is 180 but delivery got created for 200 qty. It is not even that when the delivery was made there was sufficient stock and It is happening for a few materials. Is there a configuration which allows delivery to be made for greater qty than unrestricted. If not, what is causing this strange behavior of stock? Kindly enlighten.