QTR-Quadtone RIP

Dear Group

My problem is as follows (please excuse my not so perfect English):

From the beginning of curve creation, the K ink comes too late. The 
first greyscale after calibration and measure of the patches (according 
to QTR helpguide, and with the help of a Techkon desitometer) is 
totally smooth, except for the K flushing in and creating a 
steep "jump" from the 90 patch up to the 100 patch. I tried with K 
inklimit and grey curve, but the problem remains. As soon as I 
linearize (which I did even though the scale was not in any way 
perfect), the scale gets smooth, but with two "jumps" around 85 and 35. 
On the prints, the practical relevance of the problem appears to be not 
a desaster, but I want to have it perfect now! :-)

Can anybody help?
Thanks a lot
Alexander