Here's the thing.
Once any kind of hard copy paper trail printer is no longer directly connected to the selection controls the only assurance you have that who you chose is who was recorded is the software controlling the process.
Which is the thing people are concerned about.
BTW even if the code shows they are linked the obvious tactic is to "pre load" or "post load" a bunch of votes for a candidate before or after the official voting process.
A thoroughly corrupt design would allow this through a separate data port to speed things up.
My instinct is a "voting machine" should be as simple as possible. It's reporting to the final tally should be secret (so no one knows the result early) and incorruptible (so it can't be changed)