Actually it does — because the law is not valid.
That's right, it is a legal non-entity.
Why?
The Constitution speciffically prohibits laws of an Ex Post Facto nature to both the federal government and the states; even with the Supreme Courts considering this restriction only upon criminal laws, that this increased the punishments of those already tried and convected makes it ex post facto.
If a state changed its laws to take away felons right to vote and applied it retroactively to already convicted felons it would be an ex post facto law.
There is nothing unconstitutional about making removal of voting rights an additional punishment for felons before they are convicted.