I have a recurrent problem with my Auction House sales. The thing is that I receive a mail saying that my sale has been succesful and that I will receive the money in the short term, but I never receive the money, nor my items back.
You can see some screenshots below. Maybe it is only a coincidence, but the "bugged" AH sales come from the same 2 characters. Are they cheaters?
When you sell something, you get that message first and in 1 hour you get another message with gold. First message does not disappear. The 2 messages at the top still have red timer near them, it means the gold has not been sent yet. But you should have received gold for the other 2 in separate messages already. If there were any other messages with gold, it was those.
Are you sure you did not take any gold at all from mailbox before making the screenshot?
There have been forum threads about this before so such problem exists. But I have never noticed it happening to me. The only thing you can do is reporting it on bug tracker.