That is the way the slider works. It doesn't bother me so much as I only use it as an adjustment method of last resort.
My preferred tool for adjusting white balance is the 'click' tool. If I can find the right white or grey tone in my image, then I always get the best results with this tool.
If I'm not happy with the results from the 'click' tool, my next step is to try the different "Daylight', 'Cloudy', 'Shade', etc. presets.
If neither of the above work, I will use the color temperature slider, then use the color tone slider, if necessary, to correct any color shift. Actually, you can do both of these at once with the color wheel tool (the 'tune' button) but I prefer to do them separately.