David Stiff, writing on Standard & Poor's HousingViews blog, says banks appear to be the answer to a question  many people raised about why Atlanta had an out-of-proportion fall in home prices as shown in the most recent Case-Shiller index.

"According to the latest S&P/Case-Shiller Home Price Indices report, home values in Atlanta fell 5% from September to October and 11.7% from October 2010 to October 2011," wrote Stiff who is chief economist for the Case-Shiller Index, which uses market data from Fiserv.

The answer turns out to be what banks are doing.

"Taking a closer look at Fiserv’s real estate transaction data for Atlanta, I determined that there was a significant increase in the sales volume of bank-owned properties in August, September and October in the Atlanta metro area," Stiff said.

In addition, Stiff explained, banks do not stop selling when the weather cools, so sales of bank-owned properties tend to make up larger proportions of the overall sales during those months.

The bank-induced fluctuations have been going on in various markets since housing prices began to collapse, though not in any consistent pattern.