Then, with the help of a lawyer from South Brooklyn Legal Services, Mr. Sarmiento began turning over some stones. He found that MERS might have violated tax laws by waiting too long before transferring his mortgage. He also found that MERS could not prove that it had transferred both note and mortgage, as required by law.

One might argue that these are just legal nits. But Mr. Sarmiento, 59, shakes his head. He is trying to work out a payment plan through the federal government, but the roadblocks are many. “I’m tired; I’ve been fighting for two years already to save my house,” he says. “I feel like I never know who really owns this home.”

Officials at MERS appear to recognize that they are swimming in dangerous waters. Several federal agencies are investigating MERS, and, in response, the company recently sent a note laying out a raft of reforms. It advised members not to foreclose in MERS’s name. It also told them to record mortgage transfers in county records, even if state law does not require it.

MERS will no longer accept unverified new officers. If members ignore these rules, MERS says, it will revoke memberships.

That hasn’t stopped judges from asking questions of MERS. And few are doing so with more puckish vigor than Arthur M. Schack, a State Supreme Court judge in Brooklyn.

Judge Schack has twice rejected a foreclosure case brought by Countrywide Home Loans, now part of Bank of America. He had particular sport with Keri Selman, who in Countrywide’s court filings claimed to hold three jobs: as a foreclosure specialist for Countrywide Home Loans, as a servicing agent for Bank of New York and as an assistant vice president of MERS. Ms. Selman, the judge said, is a “milliner’s delight by virtue of the number of hats that she wears.”

At heart, Judge Schack is scratching at the notion that MERS is a legal fiction. If MERS owned nothing, how could it bounce mortgages around for more than a decade? And how could it file millions of foreclosure motions?