I had this problem with some DMX dimmer packs years ago. Solved it by adding a night light to the same channel as the lights. The night lights would glow softly when the channel was off, and the LED's would not turn on until they were supposed to. Although, I know that (at least the new versions of the express) have some sort of circuitry built in to take care of this problem. What version express are you running? Are you using LED's or incandescent?