Why does AP write ledes such as this?

NEW YORK - U.S. home prices plunged by a record 8.4 percent in November, marking two years of slowing returns, according to a key index released Tuesday.

It's simply not true. Home prices did not fall 8.4 percent in November. They fell 8.4 percent over the 12-month period that ended in November. AP does this all the time. By declining 8.4 percent in one month, home prices would have been falling at 65 percent annual rate. If you think the Fed is panicked about an 8.4 percent annual decline in home values, think what they would do about a plunge at a 65 percent annual rate.

AP's second sentence does clear things up: "The decline in the Standard & Poor's/Case-Shiller 10-city composite home price index was the biggest year-to-year drop since a 6.7 percent decrease in October." But why couldn't they say "year to year" in the lede?