Assuming these callers were telling the truth, my personal suspicion is that we are dealing with people who can't work touch screens, due to the inability to adjust for the difference in the projected image and the touch part for that image generated by observation angle.

I'm usually behind at least two people like this when I'm at the ATM machine.

Heck, when I run across one of those horrible systems where you have a typewriter keyboard projected on the screen, and you have to actually type something, I have a lot of trouble myself.

The key thing is, if you don't get the result you want on a touch screen, you stop and do it again. There's no excuse for allowing an erroneous vote to be actually registered.