D800 matrix metering vs. D600 matrix metering.

The "why..." is what I show in (4), the chess board example keeping exposure in Matrix.

Re the extreme case of a very dark frame with one strong light I guess I just prefer the way the D600 does it now. Looking at it from a realistic POV, for this effect to happen the background had to be so dark, that if my subject was in it I probably wouldn't want to take the photo. I could barely even see what I was shooting.

Most of what I shoot is concerts in very poor and/or low light. So far, in every case where a subject had (even very) weak light and there was a strong light (usually a spotlight) in the frame, Matrix worked very good. I often use e.g. f/1.8, ISO 6400 and hope to get 1/100. I consider this very low light. For the "problem" to happen I needed my subject/background (i.e. everything other than the lamp) to be significantly lower lit than this.