Ted Selker, the co-director of the Voting Technology Project being conducted by the California Institute of Technology and the MIT, has one possible explanation: Experiments show that voters incorrectly choose a candidate on their ballots one in 30 times, even under laboratory settings. "People are just sloppy and make mistakes," Selker said.

Voters may interpret the problems as an issue with the e-voting machines, Selker said. But much of the problem may simply be related to how voters actually use e-voting hardware. Touchscreens are designed for tapping, he said, while voters will often try to drag their finger across a selection, as though they are dragging a computer mouse.

"Vote flipping is a user interface problem," not a technical flaw that is allowing votes for a candidate to be miscast, he said. "I trust that that is not what's happening."

Machine calibration can be a problem because the units are sensitive to user finger inputs based on the user's height and other factors. Taller and shorter voters -- outside of the calibration settings -- can affect the areas where their fingers meet the touchscreens, causing selections that appear to be incorrect, he said.

Better machine designs and simpler voter selection processes, through improved and more intuitive designs, would help a lot, said Selker, who is also a professor of media arts and sciences at MIT and an expert on product design and human interfaces.