Make sure when you use it to turn off the Pixel-Shift You can only process Pixel-Shift with Pentax software.I rarely use Pixel shift though if On1 added pixel shift capability to their software that would be different.
My system is a little older than yours and Win 7, but if you like I can try shooting some PEF files with my K-1 and see if I get something similar. It might be worth trying some images shot as DNG to see if you're getting the same problem. I don't get this problem but then I shoot a K-1 and use DNG. Could it be the highlight indicator for over exposed parts of a scene? This is normally red so I'm guessing not. See the screen shot:I can't say I've ever seen that before, it's like there's a luminance mask with a colour palette. Tired of dealing with them, slow as molasses to respond. They keep asking for more information when I submitted a trouble ticket.
I have had hints it could be a display card problem on my MacBook Pro mid 2014.
I've been using On1 Photo RAW recently, and have a problem with the results: There is a pink color in some of the brighter portions of my image, but it's not in every shot and only with 645Z. I LOVE, I mean LUV my 645Z and use DxO PhotoLab to process my RAW files, which gives excellent results.