I tried bidirectional tracing on an interior scene. First problem, walls was white but its orange in a scene (standard computing or RT was fine), dont know why.
Then after few seconds VRay and Max crash 
I think multi/sub object not working in bidirectional tracing. Is it ok?
(I am sorry! Now How to use VRayBPTracer was found!)
It seems that VRayBPTracer (Beta3) is not supporting multi/sub of max.
and VRayMtl fog, VRayLightMtl is not supporting.
Thanx
And will be multi/sub material supported?
Yep, it will be supported.
Best regards,
Vlado