Bug? Account credit balance applied twice on one transaction

Here's the scenario - once upon a time, we treated deposits as payments on account. This resulted in credit balances that were usually zeroed out when the merchandise was invoiced. We have since switched to using work orders and order deposits but there are still a few of the old credit balance accounts out there...
Transaction details: customer has a $200 credit balance. The invoice total is $538. When tendering the transaction, we tender $200 to account type '90 Days Same as Cash' (this will zero the credit balance) and $338 to COD.
OK, I'll admit that this is a strange situation.
The result - two tender types (90 Days Same as Cash & COD) that BOTH show a $200 credit balance and an INCORRECT bottom line transaction balance of $138. The customer account balance is correct at $338.
I realize that if I had tendered the entire $538 to COD that the transaction balance would have been correct.
RMS should not have applied the same credit twice on a single transaction.
It appears as though you can create and name as many account types as you'd like but that in the end it's all thrown into the same pot. The separate account types are not tracked separately. I consider this a major shortcoming.
The worst words in business: 
"We''ve always done it that way"
Reply to
Terrible Tom

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