The problem has been reported in U.S. elections since 2004 as states move to e-voting in an effort to make the vote-counting process more accurate. Instead, for many Americans, the change has led to more questions than answers, and suspicions that their votes aren't being counted correctly.

But is vote flipping a real problem, as e-voting critics argue? Or is it caused by user error, machine calibration issues or other factors, as e-voting advocates argue?

Stanford University computer science professor David L. Dill, who founded the nonprofit Verified Voting Foundation and VerifiedVoting.org, has been looking at vote flipping and yesterday called for investigations to determine if there is a real issue.

"People have been way too quick to diagnose the problem," Dill said. Some who have not examined the issue closely quickly call it a touchscreen calibration problem, while others point to different causes. "It could be a calibration problem with the touchscreens, but I'm not sure that anyone really knows yet because no one's looked at it. My answer as a computer scientist is that I want facts ... and all I've heard for two years is speculation."

Dill rejected one theory -- that the problem is a conspiracy to defraud voters of their votes and give the election to the opposition. Once a voter picks a candidate, a review screen shows who they voted for. That ability to review the vote before it is ultimately cast, he said, makes it less likely that fraud is involved.