This is a great point. Often this issue is not raised due to necessity of coercion resistance which prevents voters to prove how they voted. In absence of such

This is a great point. Often this issue is not raised due to necessity of coercion resistance which prevents voters to prove how they voted. In absence of such requirement voters may as well be able to issue a message which invalidates the vote and can be collected by a third party. Then the invalid votes tallied collectively could be used as legitimate reason for nullifying election result.