As per statistics, Median Prices are dropped as follows. http://www.dqnews.com/Charts/Annual-Charts/SDUT-Charts/ZIPSDUT08.aspx

Oceanside S 92054 -25.6%
Oceanside E 92056 -24.9%
Oceanside N 92057 -35.6%
Oceanside C 92058 -21.6%

I believe drop in median price is because of drop in home price and shift of buying trend to lower priced homes.