Even in a broadly declining market there are sometimes month-to-month fluctuations in the median price in some zip codes that show a positive change.

For example in the data cited below there is one zip code in Escondido (92029) that showed a 11% increase in the median on a mere 12 sales, while all other surrounding areas were off significantly. http://www.dqnews.com/ZIPSDUT.shtm

Monthly stats are very misleading because they vary widely. If you plot a time series for a particular zip code you get a better feel for the monthly variations and trends.