With the arrival of the latest Hearthstone expansion, Whispers of the Old Gods, a lot of Classic and Basic cards were changed. Recently, Blizzard has announced that the increased disenchant value of those cards is soon to be gone. You can find the list of those cards at the official blog page. Don't miss the huge amount of Arcane dust that you can get from disenchanting. It is more than 2,000 dust. You can craft an additional Legendary card with such amount of dust!