Glenn Burnage has kindly sent me the patent info for the adjustment device, which includes a useful drawing. My theory is lack of lubrication and/or roughness between the female cone of the adjustment collar and the male cone of the clamping ring. When you slacken the collar, it needs to slide around the collar and if that is too tight you are in trouble. Also, if you pull on the wheel, as one tends to do when leaving the car, that will tend to jam the clamping ring further into the collar, exacerbating the problem. So leaving the splines unlubricated is probably a good idea, to minimise the chance of the wheel hub edging outwards when the rim is pulled.