The system always clears the Partial pay bucket every time a full payment amount is made (satisfied). This is done regardless of whether the due date moves forward or not. For example, some Delinquency Control settings might allow a due date to be moved forward so the member is paid ahead, others do not. But regardless of that, the system always clears the partial pay field whenever it sees a full payment amount has been received.
When it comes to the Partial pay field, extra money included with a regular payment behaves different from extra money (whether below a regular payment amount or not) paid independent of a regular payment. If a payment is made during the payment period that includes extra funds over the regular payment amount, that extra is NOT remembered toward the next payment. (Since you’re also fulfilling a payment at that time, Partial pay is cleared automatically.)
If you pay a little bit every week, the partial pay feature keeps track up to the point when a full amount is satisfied. (This helps members who like to pay little bits at a time, to stay caught up.) Just remember that because of the way the calendar falls, every so often the timing might work out to bump the due date sooner than you might otherwise expect.
NOTE: The Partial pay field is NOT used when processing payments for mortgage loans with the 360-day interest calculation type. Also, for online credit cards, once the payment has been fulfilled for a period, additional funds will not accumulate in the partial pay bucket until a new calendar month begins.