Can I process vendor bills if the PO is put to delivery complete(short closed)..?

Hi All,

• I have released PO#4500000001 for 2 units of X.
• Subsequently 1 unit of X is delivered in my plant against this PO and bills against the GR are not booked.
• Due to some undisclosed reasons, I have put tick mark to delivery complete indicator and PO has gone for versions, followed by amendment release.
• In this stage system is not allowing us to process the bills against the GR which is already posted unless the amendment is released.

Is there a way out of this situation, where we can still process bills even if PO is short closed...?