Kevn McCrea explains how that could happen - basically, commericial property values are plummeting even faster than residential ones:
The result is that residential taxes will rise, perhaps substantially, even if home values continue to deteriorate in 2009. Successful lawsuits from owners of larger commercial properties may exacerbate the shift of tax liability from commercial properties to residential properties in 2010 and beyond.
Because, remember: Prop. 2 1/2 only limits the total amount of money a city can take in in property taxes, not how much an individual property owner pays.