Buyer paid invoice twice, I refunded once now invoice shows credit owed to buyer?

[Vengeancetfn]

We have sold to the buyer in the past.
sent the buyer their invoice.  The buyer paid twice, the second payment was made within 10 seconds of the first.
We alerted the buyer, who was greatful and we refunded one of the transactions.   The invoice now shows that there is a credit owed to the buyer.   The buyer paid with the same login email address as previous transactions with us.  one payment trasaction detail shows the buyers email as convirmed and verified, the other say the same email address is not verified.   
Called PP customer service.  They said that this would fix itself when the refund was applied...lol    

WTF is going on?