When thumb of USlider get off the panel area....

I have a problem, I’m developing Option that is one of game features. the option feature has been developed to be maintained each setting value if the option window is restarted.
But If I pull the thumb over the end of USlider and out, the thumb move to ‘0’ position of USlider. And when I pull the thumb inside the panel, the thumb locate actual value position.
I would like to maintain the thumb position of USlider when the thumb get off the panel area.
guys, what should I do?