In daily use of the Mental Ray renderer I noticed a energy inconsistency while playing with local vs global sampling... I was quite bogused by this and decided to test it out a little further.
You can see by the attached imaged that:
(1) Energy is higher with 1 eye ray then with 64 eye rays per pixel
(2) When there is 1 ray per pixel and varying number of local glossy reflection samples energy stays consistent
(3) When there is 64 rays per pixel energy increases as local reflection samples increase :