Unable to reproduce.
I just tried it here with a D700 file (e.g., set all HSL sliders to -100, and choose Save New Camera Raw Defaults from the flyout menu). The default stick.
What steps did you take on your end?
I think I discovered the problem. I have the RAW converter set so the default is ASA specific which is how I have the defaults set for my D200, but I did not set defaults for every ASA of the D700. I noticed that nothing is sticking in the images I tried, but they were not shot at the same ASA as the image I used when I set default. I tried it on an image that was shot as the same ASA and it worked correctly. Thanks for the response.