The Use Tax Accrual feature creates distributions on transactions entered in the Payables Transaction Entry window.
If you open the Payables Transaction Entry Distribution window prior to zeroing the Tax field and/or entering the vendor's billed tax amount into the Tax field, then the distributions will need to be defaulted manually to get them back in sync with the face of the document.
To avoid this issue, do not open the Payables Transaction Entry Distribution window until all changes to the Tax field on the Payables Transaction Entry window are complete or if you do, open the Payables Transaction Entry Distribution window again after all changes have been made and click the Default button.