@Maverick2  RE: I choose to leave the credit to be used later. QB tells me a credit memo will be created. Which it does... BUT

It doesn't tell you a credit memo transaction will be created. It says a credit will remain on the customers account. These are not the same thing.

The "Credit Memo" button the the message creates a printout showing the over-payment, but it's not really printing a credit memo transaction. (It's a button label only a product manager could love, and not anyone familiar with actual accounting.)

The credit referred to is the unapplied/open balance on the over-payment received. Since there is nothing else to apply the over-payment to, the customer will have a credit / negative balance after recording the payment. 

Adding an actual credit memo transaction in this case would cause the customer to have even more of a negative balance.