alt Hacker NewsThis problem is unavoiable as you ultimately have to trust the root, just like with paper ballots, so this is not an applicable problem. Although you could include encrypted metadata for location, id number attached to a real person and other information that would make verification after the fact much, much easier.
The problem of addition (or deletion) of votes is solved by having a paper pollbook to go with an electronic pollbook, plus doing reconciliation.
Election integrity is about finding all the attacks that can reasonably be expected, and detecting or -even better- preventing them. But it's a tougher problem than this one-sentence summary makes it sound.