Probably a new AH bug instead of a ATT bug, but when mouse over items in AH that has more than one version (e.g. transmog that has the Normal, Heroic and Mythic versions) the tooltip isn't correct identifying which version is actually in AH. Just bought an item that I already had because of that.

Unfortunately, this is a known issue in Blizzard's auction house revamp and not something we can address directly.