the star nut does not provide any gripping force to the stem...something else is wrong. I tried one of those adapters once, it was a piece of garbage. might not be the same one you have, though. is the wedge aluminum? if so, that might be the problem... you might think it's slipping on the 1 1/8 part, but it's really the quill part that's tuning.
regardless, the star nut won't make a difference.