Hi,
I have such problem.
Here’s the example of the scene:

By deathevor at 2011-02-10
I’ve used mr Sky Portal and rendered it with Mental Ray (Final Gather and GI ON).
I also rendered Diffuse and Shadow pass, and everything worked ok.
But, my aim is to render the same image with Matte/Shadow/Reflection Material on the ground plane. (For later compositing on to Video footage)
So that what I get.
- Rendered picture - Ok

By deathevor at 2011-02-10
Here’s an Alpha channel for it. And first problem is that it doesn’t have the area with reflected light in the front of the cube.

By deathevor at 2011-02-10
-
Shadow Pass - Fail
(just empty RGB and empty Alpha channels)

By deathevor at 2011-02-10 -
Diffuse Pass - Fail
(Some glitches + Shadow pass)

By deathevor at 2011-02-10
And basically the alpha channel for Diffuse pass is the same as for Render

By deathevor at 2011-02-10.
So really I can’t make it work at all. I’ve tried with different lights (Phonometric, Daylight, Standard lights), with FG and GI off, different materials(Standart and Mental Ray) . But still the same result, Diffuse contains shadow pass and Shadow pass sometimes has some information, but mostly it’s glitches.
Does anyone can suggest the way to make it work?
I also want to ask about this - Which Pass should I use to render this part separately from others? (I will remind that on Renderer and Diffuse pass the alpha didn’t contain this area)

By deathevor at 2011-02-10
Thanks