Paying Off a Balance of Open Invoices While Purchasing Store Credit Produces a Bad Invoice

We've now resolved the incident.

Frequency: Low

Description: When paying off a balance from one or multiple open invoices and simultaneously purchasing store credit for a customer's account, the invoice for the purchase of store credit will show the total amount paid, even though the amount of store credit purchased on the new invoice was less than that amount. However, the open invoices which were just paid were paid correctly.

Example: A customer came in to pay off their last two Daycare invoices for a total of $60 ($30 each). They also want to purchase $15 of store credit to place on their account for their next visit. I add the customer's open invoice balance to the shopping cart, and then add $15 of store credit to buy and add to the account. After checkout, I can see that the two old Daycare invoices are paid correctly, but when I view the new invoice for the purchase of store credit, I see that the grand total of charges is $75 (the total, combined payment that the customer was charged).