i had the same problem on mine and it took me ages to figure out, essentially its a piece of plastic between the contacts!
if you tug on the actual plastic slider switches that you can move to select which light comes on and if it comes on when the door is open they should come off. (be carefull though theres a spring and tiny bit of metal that can go flying and is a pain in the arse to find if it does)
In there you'll find a string and lil piece of metal as just mentioned, that spring and piece of metal should move up and down within the little switch smoothly, if it doesnt thats your problem, take the spring and metal contact out of the switch and just file down the flimsy plastic where the spring and contact sit, which is stopping it moving properly, then put it all back together!
Simple! you dont even need to remove the light from the ceiling!
Hope it helps!
Donny
(Now can someone help me with my post please!)