I can add that I used to work with Adobe Camera RAW CS6, and it was present there as well. Skies tend to be overexposed relative to the rest of the image and skies tend to be blue, so I often tried lowering the blues. This was particularly evident if I worked on B&Ws. The Adobe method was to alter the hues and then convert to B&W, so even in a B&W, one could lower just the blue areas. PL 2 didn’t support this, but with the new HSL tool in PL 3, one can do something similar (start by reducing the global saturation, then work with the individual colors–but don’t change their saturation!).
Here’s my theory of why the HSL tool is blotchy and the exposure tool is not. The exposure tool works on all colors equally; the HSL tool will darken the colors that are closer to blue more. By lowering blues with the HSL tool, you enhance the artifacts created by the demosaicing; in other words, while the color looks uniform at brighter values, the HSL tool sees different blues and darkens them by different amounts. The more you darken the blue, the more you bring out the differences. The exposure tool works on everything the same way–the drawback is if you really only want to darken blues, the exposure tool won’t respect that.