New code can share the same bugs and add new ones.

The point here is that voting machines must be open source and its hardware completely public to analyze it. This can't be the weakest link in a democracy.

Open source software is certainly preferable to closed, but it's not sufficient for a voting machine, because there is logically no way for the user to verify that the software on the machine is what it is supposed to be.

Nor is there a way for the voter to verify that the machine itself is what it's supposed to be.

Now, if the hardware instead

1) could be provided by the voters themselves,

2) was easily auditable

3) was used in their daily lives providing a ubiquitous understanding of the technology involved

only THEN would it be appropriate for use in elections. So far, only pen and paper fulfils all of those criteria.

It also needs to be anonymous to prevent people buying or coercing other peoples votes.

and if you satisfy all those requirements, and other, congratulations, you've probably just invented the worlds most expensive printer.