If these are touch screen machines, I think the area of the 'button' image sometimes doesn't match the touch sensitive area. WHY they don't match is another question. I had this happen to me a while back. They moved me to another machine, but I don't know if they took it out of service.
While my problem was going on, some moron poll worker helping a woman yelled out to the supervisor, "This lady wants to vote for xxxxxx but the machine records it for the other guy." She blabbed this woman's vote to everyone in the place! You could hear several gasps when it happened.
Funny thing was that I was voting for an R and got a D, while the other woman was voting for a 'D' and got an 'R.'
That is the second mention I’ve seen about touch screen machines. OK, I get the calibration issue with that. Why do we need such expensive technology for voting machines? Sounds like a waste of taxpayer dollars to me.