Question on voucher close

Hello,

We are on PSOFT 9.2. One of the 3 way- PO vouchers (matched, posted) has the payment schedule cancelled on 3/31. So, there is another open schedule with schedule due date of 3/30/2023. The accounting entries for payment cancellation are available in the voucher accounting line table for 3/31/2023. I am trying to close the voucher manually through Add/Update> close voucher page. The manual close date field is already populated with 3/31/2023 and is grayed out. The goal is to close the voucher in April but I am unable to edit the manual close date. Is this working as designed ?

Thanks,

Debolina