After the ship rolls over, I noticed that there are several chairs still on the floor (now the ceiling). You would figure that they would fall down too! They weren't very close to the tables, so they shouldn't have been bolted to the floor.
Sorry, but this isn't a slip-up...it's actually attention to detail. On board ships (at least the big old passenger liners like the Queen Mary, on which the Poseidon is based), chairs are affixed to floor via a small length of cord running from the underside of the seat and attached to the floor directly beneath it. Some chairs obviously came loose in the violent capsizing, but those that didn't dangle suspended from their cords, as they would really have done had a ship like the Queen Mary (or any of her contemporaries) rolled over.