If the machines have touch screens and I assume they do the screens can be out of calibration where the active layer is not aligned with the visible button.
And this might be set on purpose too...
Even if you thought it flipped the vote don’t you get a chance to review it before your vote is locked in?
How many times have you typed a reply on FR and then when you have to go to the mandatory review you see that YOU accidentally made a typo? Could be what is happening.
My daughter worked at the test calibration and verification center when she was in college. They had teams that drove around the state and connected machines remotely to verify them for acceptance by the State of Georgia. She had all kinds of inside knowledge about the Diebold voting machines.