When doing Sales or Purchase confirmation a form dialog is opened (dialogs extending FormLetterServiceController).
If the user clicks the Batch button and enables Batch processing, the confirmation is run in batch.
Next time when the dialog is opened, if the user does not click again the Batch button, the confirmation is not run in batch, even the SysLastValue has Batch processing = yes.
This functionality is the same from R3 to latest D365.