While Blizzard has yet to make an official statement on the matter, user Rushster published a post yesterday on IncGamers.com's Diablo page about a rather dastardly exploit making its way through the Real Money Auction House.
Rushster writes that the exploit, which was created with a HEX editor by some clever users, "messes with the Auction House UI and system time" effectively allowing players to nab an item at the starting value, rather than the buyout value, by switching around the buttons. The poster has not tested the exploit and cannot confirm whether or not the issue has been resolved, but says that the exploit is very real and had already been appearing in the Auction House for over half a day.
What can be said is that the original thread which appeared on the official Diablo III forum was deleted by Blizzard rather quickly. However, users at Blizzhackers have been sharing information on the exploit as recently as yesterday, although whether or not the bug has been hotfixed since is not clear.