AP - Invoice line amounts are editable on an invoice in balance, validated, accounted and paid

 hi Folks,

The line total amounts are editable on balanced, validated, accounted and paid invoices.  The Distribution line is not editable but the line total to distribution total is out of balance which lists the general summary view as out of balance.  No system holds are applied to the invoice.  These fields should be locked down as not editable, the same as distribution lines.

Could you please tell me how to lock these fields, and/or if this is a bu g and not standard functionality.

Thanks,
Aditya