OK, so when you move the slider, are you hitting the Check mark after? Is so, does the number beside the slider show the clock offset? For instance if I click on the number (not using the slider) and then enter 100 and click the Check mark, the value stays at 100.
Edit: I just had a look at your picture, that's a pretty old card and it's been awhile since I overclocked something from that generation. I think I was using Precision (which was the same as Afterburner back in those days) back then. I can't remember, but I think that the sliders showed the absolute clocks rather than an offset clock. Can you take a screenshot of Afterburner with everything at default.