Blender 2.65 Cycles shadow pass w/ Emission from planes

Hi guys!

I have a question about shadow pass using planes with the emission materials as lights. Is it even possible?
I’m asking this, because every time I render a scene with planes as lights, the shadow pass comes up completely black, as if there are no lights in the scene. However if I use lights, it works normally. Can I fix this using planes as lights, because I don’t want to relight my scene?

Using a plane with an emission material as a light:

Using a sunlight light object:

Thank you for your help!