In my Completed tab, I had a Purchase Refund. I did not get a failed purchase. Where did this come from?
You can get purchase refunds for two reasons:
Basically, these are due to trades made between the time you saw the price of whatever you bought in the AH and when you clicked the buyout button. Since the AH does not automatically refresh, there could be a significant difference between what you can see and what's available (though you can get a different "That item is already bought" error depending on the timing).