Analysts expected Case-Shiller Home Price growth to continue its modest deceleration in August (the latest available data in this heavily lagged and smoothed data set), but the result was a doozy: the 20-City Composite index tumbled 0.44% MoM, far below the 0.20% expected increase, and a sharp decline from the downward revised 0.19% increase in July; more importantly, this was the first sequential drop in home prices tracked by Case-Shiller since March 2012, or ten and a half years.

On a Y/Y basis, home prices rose just 16.06%, down from 18.66% YoY in July, and missing expectations of a 17.1% increase. The headline national average price index rose 15.77% YoY in August.

Comments confirmed that the mood is dismal and turning uglier by the day: "Although U.S. housing prices remain substantially above their year-ago levels, July's report reflects a forceful deceleration," says Craig J. Lazzara, Managing Director at S&P DJI.