These are the steps, as I manage to track them:
- Played Narain Soothfancy, which at some point during the game, offered a copy of incoming Puppet Theatre;
- Played that upfront copy of the Puppet Theatre, copied a card from rogue opponent;
- A copy of 1/1 Zilliax was put in my hand;
- I could not play that copy at all during the game - I could “highlight” it in my hand and make it stick out above the other cards, but I could not play it, ever. And yes I had mana;
- Some turns later, I used the same Puppet Theatre, the last charge available and copied another minion, and again I could not play it, and it stayed in my hand till the end;
- Both the “natural” copy of Puppet Theatre and the one hidden in the ETC behaved normally, and allowed me to play the copied minions.
I have saved a firestone replay of the game, but not allowed to post links.