Purchase Requisition going Over Budget

We currently set up budget for purchase requisitions at the Business Unit level using Job Cost Budget Set up.

We have been facing this issue wherein a lot of times the purchase requisitions go on budget hold even though the budget amount set up at the Business Unit level ( against which the requisitions were created)  in Job Cost Budget set up is not crossed over.

We found that some of the requisitions created against the Business unit were cancelled and when a new requisition was created , it went on budget hold because it seems the sum of $ amount of all the requisitions ( cancelled and valid) is being taken into consideration for the new requisition that is created. Is there a way to fix this problem ?