Tried to install newest beta (Krakatoa 1.5.2.41471) and it seems matte objects didn’t appear when rendered from Vray Physical camera 
It is planned some updates on this?
Btw, max 2011 x64, vray 1.5 SP5
We are using the same version of VRay (but a slightly newer build of Krakatoa, of course) and I have no issues with matte objects and VRay Physical Camera here. Can you create a VERY simple scene with one PRT Volume from a teapot and some matte geometry in front of it, with a VRay Physical Camera in the view to illustrate the problem?
If it renders correctly here, it could be a problem in the Beta you are using that is not present in our internal build.
If I can get the same result as you, we can look for the problem…
Thank you in advance!
Just tried, your situation is ok.
It seems that problems is with group tool (isn’t my idea to use groups, I swear 
)
Bobo, could you try this:
Group 2 objects -> create named selection set (from max) -> add it to krakatoa matte list = rendering with VrayPhysicalCam matte failed.
After trying this a lot of times, I have and properly render too, sometimes just one object from group appear correctly in matte, but I still can’t find whats EXACTLY going on… one thing is clear - I have this ONLY with Vray camera.
Back to testing…
*I created a PRT Loader with some particles.
*Created a VRay Physical Camera for the current view
*I created two spheres in front of the particles and grouped them together
*I selected the group in the viewport and made a “mattes” NSS in the Max list
*I added the “mattes” NSS to the right list of the Matte Objects rollout and enabled Matte rendering
When I render this, I get correct mattes.
That being said, it is possible that something in your scene is causing strange behaviors in your matte objects, I just cannot tell without seeing an actual scene. If you can repro the problem using simple objects (PRT Volume and spheres) and send me the file, it would be much easier to figure out. Is there anything else in the matte objects animation? Keyframed animation, modifiers, space waprs? Anything else worth mentioning that could be a factor, even if totally obscure?