Had a light with one master switch and two three ways. My guess was that someone wired a single pole in series with two three ways. It took me a couple hours to figure out what was going on. But what I found was it had a double pole switch installed instead of a four way switch. They look the same so I can see how someone could have mixed them up easy. But my first clue should have been the off/on label on the switch. A four way or three way doesn't have an off/on mark. So I bought a four way, swapped it out and it works good.