After a series of tests on e-voting machines, a U.S. government auditor still doesn't know what contributed to 18,000 unmarked ballots in a Florida congressional race in 2006.

The U.S. Government Accountability Office (GAO) checked the firmware and the ballot display and ran calibration tests on a sample of Election Systems & Software (ES&S) iVotronic e-voting machines, the agency said in a report released Friday. Those tests, combined with others done by the GAO and state of Florida, "have significantly reduced the possibility that the iVotronic [machines] were the cause of the undervote," said the report, authored by Nabajyoti Barkakati, acting chief technologist for the GAO's applied research and methods division.

The GAO believes the ES&S machines have been adequately tested, the report says. "Given the complex interaction of people, processes, and technology that must work effectively together to achieve a successful election," other factors, including intentional undervotes or ballot interaction problems, may have caused the undervote, the GAO said.

Democratic candidate Christine Jennings lost by 369 votes in the 2006 13th Congressional District race, but more than 18,000 people who cast votes in other district races failed to have votes recorded in the congressional race. About 4,000 more votes were recorded in the Sarasota County Southern District Hospital Board election than in the House race.

Jennings is again running for the congressional seat this year.

The GAO report "leaves most of the major questions unanswered," said the Verified Voting Foundation, an advocacy group critical of e-voting machines. The GAO report didn't address potential problems with touch-screen sensitivity and low batteries, or reports of undervotes in other races, the foundation said in its own report, based on a leaked copy of the GAO report.

"The GAO report leaves us with almost as many questions as before, and the most important one -- what caused the ... undervote problem -- is left unanswered," the foundation report says. "The nature of the complex voting system in question, and the difficulty in auditing such a system, may mean such questions will remain indefinitely, but it is clear that more can and should be done to resolve the outstanding issues."

The IDG News Service is a Network World affiliate.