These machines are not "switching votes". They're just not.
You sound pretty sure about this, but remember that according to your own belief you only think that you're right.
When asked if she is sure she touched the box for Rockefeller, she said, 'I'm absolutely positive.'" Yeah, just like a lot of users are "absolutely positive" that they did the right thing. No, they THINK they did the right thing. That's the only thing they are "absolutely positive" of.
Numeric stability is probably not all that important when you're guessing.