POS: Split payment method - Cash first

It seems that if the customer wants to pay by 2 different payment methods for the same sale (eg. half by cash, half by credit card), the non-cash payment has to be processed first, as if you select the cash amount and then click on the Cash button, it will reset the amount to be paid back to the full value of the order.

For example, for a $99.99 order, the customer wants to pay $59.80 by cash and $40.19 by credit card. On the POS payment page, I change the payment amount to $60 and then press the "Cash" button, but the payment amount is reset to $100 and it can't be changed. The only way is to charge the credit card first, but that would require the shop assistant to get out the calculator and work out the amount to be charged by card by subtracting the customer's cash payment.

It would be better if the order of payment is not limited in this way.

Thanks.