geopiet Nov 13, 2016:

Note: The system acts differently when calculating VAT depending on whether you are in the Add mode or the Update/Display mode. When you enter a VAT amount using the add search page, the system supplies the VAT line amount on the Invoice Information page, and if the amount is edited, correctly recalculates this amount. However, when you modify an existing voucher VAT amount using the Update/Display mode, the system does not recalculate the VAT line amount. Instead, it displays the difference between the header and line amounts in the Difference Amount field. - https://docs.oracle.com/cd/E39583_01/fscm92pbr0/eng/fscm/fap...