Whenever someone Buy-it-Nows an auction of mine, I get the regular (congratulatons) email but in the past couple days I've also been getting a "sorry, your item did not sell" at the same time.
For me it's just an inconvenience, but for some sellers I'm sure they clicked on the "relist this item" button that comes with the email, and relisted something which had actually sold. That would suck.
I assume other people are getting this, and not just me. I wonder why it hasn't been mentioned here yet.