But one of the requirements for the touch-screen machines -- high-sensitivity to touch so they can be used by physically-impaired or disabled voters who want to vote on their own -- could cause some of the problems experienced by able-bodied voters, Beirne said. "Sensitivity is tied to the [voting] actions that are structured for voters with disabilities, so if you have loose clothing or jewelry, it can make [an errant] selection," Beirne said. "They are designed to be sensitive."

When such incidents are brought to the attention of election officials, they usually try to replicate it so they can determine what caused it, he said. "Critics call it 'vote-flipping.' That term is used by e-voting critics to mean that the machine is trying to work independently of a voter's wishes" in a manipulative way. Instead, such problems usually go back to the local procedures that are used to verify proper machine touch-screen calibrations throughout election day.

"That's why there are procedures to follow in response to it if reports come in" about problems, Beirne said.

The Election Technology Council Wednesday posted on its Web site a list of for voters about using the machines.

Representatives of several e-voting watchdog groups, however, vigorously dispute the vendors on these issues. Lillie Coney, coordinator of the National Committee for Voting Integrity, a project of the Washington-based , said the main problem is that existing standards for e-voting machine designs have been voluntary, yielding designs that don't work well for all voters.