I have a single gang switch on the landing down to a double gang in the hallway. I have swapped the hallway for a dimmer switch. I have wired in the terminals exactly the same on the dimmer as per the double switch. When I turn the upstairs on from the dimmer, and turn up to top limit, the downstairs come on aswell! Also when both are on, I can't turn the downstairs off ! Have I got the wrong type of dimmer ?