8069 is 1/3 stop more than 6400 (100 x (2^6.3333) This would be HI 0.3 on the D800 being 6 1/3 stops faster than ISO 100.
10159 is 2/3 stop more than 6400 (100 x (2^6.6667) This would be HI 0.7 on the D800 being 6 2/3 stops faster than ISO 100
I'm guessing your camera is set to adjust ISO in steps of 1/3 stop. Nikon may not be applying rounding to the numbers.
My D800 shows HI 0.3 and HI 0.7 in both displays and in the info screens on playback when using these settings. I assume you are seeing this ISO in your post-processing software?
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