I'm here to second this. I was just in a game with some friends and someone who WASN'T controlling Mindskinner and attacking with a creature ended up preventing their damage and milling the table.
Whenever The Mindskinner is in play, any damage delt by any source to a player will be prevented and will mill the table. Even sources controlled by an opponent.
E.G. An opponent attacked another opponent, and it milled every player except the attacking player.
I'd love a fix on this as soon as possible. Mindskinner is my favourite deck and I've spent money on Cardhoarder so I can play it.
In my view, it's the entire turn it comes down, all damage is prevented and everyone mills until play returns to me. The turn after the problem goes away. Should be an easy fix I imagine.