PO in Approval Flow has all lines cancelled, still queued for approval in Held order table

A Purchase Order is created and enters the Approval flow, as controlled by the order amount.

While an approval action is pending, the originator amends the Purchase Order by cancelling all open lines.  Purchase Order amount is now zero.

The Orders Awaiting Approval form shows the approval as pending still.  I expected the pending approval to be removed.

Is this functioning correctly ?  Any ideas on a work-around for this ?

thanks

Mick