Nightmare throne destroys a card when you select to add it to hand and adds it to hand when you select to destroy it.
Bug reproduction steps
Activate nightmare throne, select to add a monster to hand or destroy it, then when asked “add monster to your hand?” Selecting yes will destroy it, or selecting no will add it to your hand
Screenshot OR error code
Selecting yes should add the card to hand and selecting no should destroy it.
What OS are you using
IOS, sideloaded from mac