[Issue] Sharpness and Noise Won't Go Below Zero in Masking [Lightroom]

When I call up Masking, the controls for Exposure, Contrast, etc. (thankfully) switch to adjust these settings for the Mask.  Most work as expected, but I've noticed that Sharpness and Noise will not go into the negatives when controlled by the Monogram... they stop at zero and will not go lower.  If I manually drag the slider to a negative number, any subsequent movement of the corresponding Monogram control bumps it back up to zero.