I just cracked open my new copy of Cave Evil and found something a bit odd with the Abyss deck. The card stock appears to be different (thicker) than all the other cards. The stack of 70 cards is about a quarter inch taller than the other decks which also have 70 cards in them. The other strange thing is the sides of the Abyss deck cards have tiny bumps on them as if they were punched out of a larger sheet of stock - none of the other cards have this, they are smooth sided.
The company who originally printing our decks mucked up 135 decks, due to a machine problem. They tried to pass them off but the cards were just too messed up. I assume your deck is one of the replacements that had to be made of the Abyss deck.
This had to be done at a different factory, according to our card manufacturer, making stock different.
This was the reason we could not sell games in December and most of January, we were waiting for the replacement deck and the replacement rule book.