QTR-Quadtone RIP

I'm trying to create a simple QTR curve. When I linearize it, I do
indeed get a much straighter luminance curve, but the dmax at
100% drops dramatically: when plotted in Excel, the curve 
noticeably tips upwards between 95 and 100, reducing the
dmax from 1.62 pre-linearization to 1.53 after.

Why is this happening and how do I fix it? 

--Daniel
PS. Gray overlap is set to zero, so I don't think it's related to the
second ink curve being changed.