Darn... all my spaces disappeared from the journal entries in the bug report. Try again:

1. Open Customer Refunds
2. New: Customer: Elec Import
3. New Credit Line: Acct: 70000. Description Late Delivery. Amount 550
4. Validate
4a. Open Customers -> Select Elec Import -> Tab Accounting
4b. Receivable -550. Must be correct.

5. Open Customer Refunds from main menu -> Select Elec Import
6. Click payment, Pay Invoice screen appears.
7. Select payment method -> Current
8. A subwindow appears with heading "Credits". The credit line appears
9. On this line enter Amount 550
10. Under the window appears payment 550. Seems correct
11. Validate the payment
11a. Reopen the Customer Refunds window. The invoice line shows Paid. Seems correct
11b. Open the Customers from the main menu -> Select Elec Import.
11c. Total receivable -1100??? While the status is Paid?
Journal items:
70000 Ventes___________550
40000 Clients_______________550
55001 Current__________550
40000 Clients__________550
40000 Clients______________1100 
The journal entries don't make any sense.
But the invoice line is set to Paid while the debt to the customer increased
Expected:
Journal items:
70000 Ventes___________550
40000 Clients_______________550
55001 Current_______________550
40000 Clients__________550

Expected: In normal Supplier payments, when we PAY, the amount to be paid
is positive. I would expect this with a Credit invoice as well. 
Expected: On the customer form Total receivable decreased by the amount just paid.


But when making a payment to a customer, the amount has to be negative, so
let us try again with a negative amount.

Repeat steps 1-4, then to 5:
5. Open Customer Refunds from main menu -> Select Elec Import
6. Click payment, Pay Invoice screen appears.
7. Select payment method -> Current
8. A subwindow appears with heading "Credits". The credit line appears
9. On this line enter amount MINUS 550
10. Under the window appears payment MINUS 550. Seems correct
11. Validate the payment
11a Reopen the Customer Refunds window. The invoice line shows Open. Not correct
11b Open the Customers from the main menu -> Select Elec.
11c Total receivable -1100???
11d So it doesn't matter whether we pay a POSITIVE or NEGATIVE amount?
These are the journal items:
Ventes________550
Clients_____________550
Current_______550
Clients_____________550
Again Current is debited, although the amount entered was NEGATIVE.
Expected: different behaviour as compared with paying a POSITIVE amount.

Ok, wrong way as well. Next attempt.
Repeat steps 1-4 then to 5:
5. Open Customer Refunds from main menu -> Select Elec Import
6. Click payment, Pay Invoice screen appears.
7. Select payment method -> Current
8. A subwindow appears with heading "Credits". The credit line appears
9. Go to Paid amount and enter MINUS 550 as normal when dealing with
receiving supplier payments. This time WE have to pay, hence the negative
amount.
10. Validate
11. Window shows now "Unreconcile", would mean the entries are reconciled.
11a Check journal items tab in the Pay Invoice window. 
11b Clients____________550
    Current__________________550
    Reconcile is blank
    Expected: The button Unreconcile not appearing
13. Open the list with Customer Refunds
13a Check status.
13b Still 'Open'. Corresponds with Unreconciled payment entries
14 Open Customers list -> Select Elec Import -> Open Accounting tab
14a. Total receiveble = 0. Expected -550 because the state is 'Open'
     Open is NOT PAID
15. Press Journal items from the list on the right:
15a 40000 Clients____________550
    55001 Current__________________550
    40000 Clients__________________550
    70000 Ventes_____________550
    State is all 'Valid'
16  Reconcile:
    Clients____________550
    Clients__________________550
17 Open Customer Refunds: status is Paid now.
Expected: After payment no manual reconciliation should be needed.