I had a look on my account and found the same thing but may it is not an issue. Because I found out when a invoice was “refunded” before the money was on my account and tagged to the invoice, it shows “credited”. But when a invoice was already paid and tagged to the invoice then it shows as paid (I think because the money was already on your account) and you have only the credit note which refers to the invoice.
So, I don’t know is it bug or not. Could you may check your account for this behaviour?
Edit: I don’t have to deal with many refunds, just a few, so it is maybe just a coincidence.
My misunderstanding of when the “Credited” flag would show up, just looked a bit strange when looking at a receipt that shows “Credited in Full” but get the jist if a payment had been allocated then that takes precedence.