Erik, the CD4082 is sold as an AND-gate. You can also call it "negative Or", if you want to focuse, that in this certain application the input signals are of negative logic, means that when a key is pressed the according row is low. But nevertheless, the gate is an AND-gate, as called by the manufacturer. It has a certain truth table and it works in Mark's application, just as expected. But you stated, that it doesn't work as AND-gate, which is just wrong.

Erik, you could have explained Mark, that there's positive and negative logic and that a gate can have two "functions". But what you did was just confusing Mark, by telling him that he's wrong and has made a mistake, what he obviously did not.

Kai