It's something having to do with the smart junction box, as I was told a couple years ago when I installed my LED's. I guess it doesn't completely cut off power like a switch does but instead leaves a trickle going to the plug, and with an LED that's enough to light it up slightly. I dunno.
I switched my dome/map lights to LED also from diode dynamics. Have had them for close to 6 months. Even when off they have the faintest of glows. I remember reading that it has something to do with the fact that the led uses such little power that even a small trickle that gets through allows it to glow. Another bulb like an incandescent for example takes a lot more power. And the trickle wouldn't be enough for it to glow at all. Basically, LEDs r really efficient
I have LED Reverse Lights. Same thing happens to me. Either they are really cheap or, like mentioned above, really efficient. I could dust of my EE coursework to find out but I don't want to know that much