Can't enter CMYK propertly, values change in all fields when values are change in any others. This results in an inaccurate profile.

When attempting to use the CMYK fields to define an object colour the values in all fields shift and change, apparently at random, when entering a new value in a specific field. As an example, if defining a colour with a CMYK profile Y-30 M-6 C-90 K-0.

After entering the values in fields for Y M and C, then, when entering a value in the field for K, all the other fields change from the original values I had set, without any additional input from me. The end result of this is a colour profile which is entirely different from the one I intended.

I have tried several times to create a CMYK colour profile to reproduce a specific colour from Trumatch colour swatches. However, as of this point in time I have been unsuccessful in doing so.
I am also curious to know if Inkscape supports pallets. I use Trumatch colours in other graphics programs and also on occasion use Pantone colours. Having these palettes available in Inkscape would be very useful, especially for creating work that is to be printed commercially.

Help with this matter would be greatly appreciated. As of this moment I can't use Inkscape to create work that defines colours which can be accurately reproduced by a commercial printer. Working on graphics for web publication is fine, however from a professional graphics point of view it is important to be able to define precise reproducible colours using universality accepted colour swatches such as Trumatch or Pantone.