WHT Tax issue noted when user is using mixed payment for customer payments received.

Problem: 
  Customer master indicated as customer has WHT implications (say 2%)
  When funds received from customer, user use mixed payment for recording payment received.
  User notice that this particular transaction did not have WHT implications as this transaction is solely for purchase of goods.
  User proceed to delete WHT tax record on invoice details under mixed payment.
  However, system did not update change, still restricted amount received at 98%. (net of 2%)
  User can proceed to post if user indicate amount received at 98%
  The extra 2% will be reflected as a CUPOA (over payment) in the customer ageing account.

But when we do this in IFS Apps 10, it works as expected and no CUPOA is created. However, in IFS Cloud, a CUPOA (over-payment) . is created — why does this behavior occur?”