In Estonian e-voting, you can vote as many times as you want, only your last vote is counted. A week after online voting is closed, there is still a paper voting day, where you can go and override your online vote with a paper vote in the traditional booth.
So they can unambiguously tie a specific vote to a voter, yet nobody is concerned about the possibilities of retribution against certain voters?
Yes, they can at some point in the flow unambiguously tie a specific vote to a voter. Postponing the "separation" to after the paper ballots have been cast is then a simple trick. How it works is they encrypt the vote (using assymetric encryption), and then sign that datapackage with the private key on your ID card.
Once the votes need to be counted, the signature is removed, and all the resulting encrypted vote data is then sent (without identifying information) to a third server which has the private key to decrypt the votes. They are decrypted and then counted. This third server has no access to identifying information. The server stripping votes from identifying information has no access to the decrypted data.
So they can unambiguously tie a specific vote to a voter, yet nobody is concerned about the possibilities of retribution against certain voters?