Apologies, I can't figure out how to say any of this concisely. To recreate: - Have an overdue item with an accruing fine - pay the fine - check in the item, backdated to before its due date - confirm that your patron shows a credit for overpayment of a fine - void your payment - confirm patron's account is not right The fine shows amount=0 and amountoutstanding = [whatever the original fine was]. The patron shouldn't owe us anything here. Further complicating things, the fine doesn't show on the Make a Payment tab at all -- seems like the logic here must be to only show fines where the amountoutstanding > amount?