An order to switch subscription service is placed. Both plans have the same recurring fee cost, refund period is equal to the period recurring fee are taken for, but the order total is not zero, refund is less than recurring fee.
Price precision is more than 2 digits, which causes a refund amount to be calcluate dincorrectly. The issue is reported as a bug with id #PBA-59929 ("Incorrect refund if price has more than 2-digit precision"), scheduled to be fixed in one of the next product updates.
Issue a credit memo to adjust customer's balance and close the invoice.