Bug 18580

the recordpayment routine in C4::Accounts cleared old paid fines and applied credit amounts as part of its pay routine. The behaviour was implicit and not signalled or commented in the code. The pay routine in Koha::Account which is now called by paycollect.pl instead of the old routine does not leaving these on the users fine display although they owe 0. Staff cannot manually remove these.

For example a user has the following accountlines
+-----------+-------------+-------------------+
| amount    | accounttype | amountoutstanding |
+-----------+-------------+-------------------+
| -1.300000 | C           |         -1.300000 |
|  0.650000 | Res         |          0.650000 |
|  0.650000 | Res         |          0.650000 |
|  0.650000 | Res         |          0.650000 |
+-----------+-------------+-------------------+

after recordpayment has been called with an amount of 0.65 the lines are
+-----------+-------------+-------------------+
| amount    | accounttype | amountoutstanding |
+-----------+-------------+-------------------+
| -1.300000 | C           |          0.000000 |
|  0.650000 | Res         |          0.000000 |
|  0.650000 | Res         |          0.000000 |
|  0.650000 | Res         |          0.000000 |
| -0.650000 | Pay         |          0.000000 |
+-----------+-------------+-------------------+
However now calling Account->pay for the same amount results in 
+-----------+-------------+-------------------+
| amount    | accounttype | amountoutstanding |
+-----------+-------------+-------------------+
| -1.300000 | C           |         -1.300000 |
|  0.650000 | Res         |          0.000000 |
|  0.650000 | Res         |          0.650000 |
|  0.650000 | Res         |          0.650000 |
| -0.650000 | Pay         |          0.000000 |
+-----------+-------------+-------------------+

leaving the credit and two fines with an amountoutstanding although the user has nothing to pay (the amountoutstanding columns sum to 0) and leading to misleading displays.

The difference is driven by the line where @outstanding_fines is retrieved the selection is amountoutstanding > 0. In recordpayment it was amountoutstanding <> 0 so that negative amounts were included and processed as part of the payment, rather than ignored. The fact that this implicit behaviour was not commented made it easy to miss.