2-Way Voucher Match, Matching Code 9

Hi

We are on release E1 9.0

I am trying various ways of redistributing a voucher using 2-way match, but cannot figure out matching code 9 - cancel balance of line.  When I use matching code 9 and adjust the 'amount to voucher' on the grid to match the 'taxable amount' of the voucher in the header of the 'Redistribute Logged Voucher - Voucher Match' application P4314, the 'amount to voucher' always goes back to the 'amount open'.  Unlike other codes such as 1 or 7 where when the 'amount to voucher' is changed it remains as the changed amount, using matching code 9 does not let me 'match'