I had the same problem on my Lanikai S-T, and tried the paper in the nut and tightening the tuner up as much as possible. What I concluded in the end was that the angle of the string passing over the nut is just a bit too low on these ukes for a low-g - the string ends up too straight. The solution I found was to attach the string much slacker, so that when you wind it on you end up with five or six winds on the capstan. That way, the string is coming off the capstan at a much lower point and making a tigher angle on the nut. Cured the problem for me.