Their story began in 2013, when the Shulmans sold their home on Hamilton Avenue in Santa Clara County to RFBPO, a Zuckerberg-owned LLC. The Zuckerbergs bought up four properties, including the Shulman’s, around their Palo Alto home after learning that a developer planned to build a home next door that would be tall enough to see into the Facebook CEO’s master bedroom.

The Shulmans purchased property in Atherton in San Mateo County and built a new home on it by 2015, within the two-year time frame Prop. 90 requires. San Mateo County assessed the new property at about $6.8 million. But when the couple applied for Prop. 90 approval in San Mateo County, they were denied. That’s because Santa Clara County had assessed the value of their old residence at just $4.9 million, a fraction of the sales price. And that put their new place well above the required threshold allowed for a property tax transfer — 110 percent of the old home’s assessed value.

With the denial of the transfer, the Shulman’s say their property taxes rose by about $60,000.

But the Shulmans and their legal team say the county didn’t fully take into account the roughly $3 million complete remodel of the Palo Alto house they did a few years before they sold it, or the fact that other homes in the neighborhood had also sold for more than $10 million. And, they said, an independent appraisal they requested said the property was worth about $6.7 million, within the 110 percent value of their new home allowed under Prop 90. So, they argued, even if the county declined to assess the property at $14 million, it should have been much more than $4.9 million.

If the county used the $14 million figure, the property would funnel well over $100,000 toward Santa Clara County.