PR Cancelled Check box did not Enabled at Header level

Hi Team,

I Created a Purchase Requisition ( PR) with Line One and Approved. Using Auto Create Created a PO and Approved PO.

Now I have cancelled PO, While PO cancellation i have sleeted "Cancel Requisition" Check box and Cancelled.

Now I can see PO Header level Cancelled Check box is enabled but PR Header Level Cancel Check box in Not Enabled.

PR Line level Check box is enabled and PR Amount is changed to Zero.

So Please let me know what is the Standard functionality. will the PR header will change to Cancelled or we need to cancel PR Manually.