For what it's worth, a month later, that refunded Southwest purchase never had the Airline Fee Credit reversed. Not that I'd recommend trying to do that intentionally (just getting it as a flight credit is a better plan in that case as someone mentioned above,) but it seemed like an interesting data point nonetheless. The particularly surprising part of it to me was that the fee credit actually posted for that transaction two days after the transaction had already been refunded. I wonder if there's a bug in their system where it doesn't detect the transaction being refunded if the refund happens before the credit itself triggers. Or perhaps it's just not set up to reverse the credit in the event of a refund, though that seems very much unlike Amex.