The darkest cloud over China is its property market. Factoring in its impact from steel to furniture, it has powered nearly a fifth of the economy. Now, it is set to subtract from growth. House prices have fallen by 6% over the past year, the steepest drop since records began. It is not the first time that the property market has looked fragile, but previous dips were driven by deliberate policies to cool the market. In recent months, it has been the opposite: demand has failed to respond to a series of boosts such as cheaper mortgage rates. This has prompted predictions of a coming crash.