Its somewhat esoteric in that it only affects those of us wishing to run a custom dpi setting of between 96 dpi and 120 dpi (100% - 125%). I happen to find 113% (108 dpi) perfect.
Basically, Diva (for example), scales properly if the Control Panel "Change the size of all items" slider is set to "Smaller" (100%), "Medium" (125%), or "Larger" (150%"). A lot of people with HD displays run 125%, which is in fact the Windows default.
However, if one checks the option "Let me choose one scaling level for all my displays" and selects a custom level of between 100% and 125%, Diva only displays at 100% (96 dpi). Interestingly, this is true for exactly 125% - works only when selected via slider (and the "Let me choose..." option is not selected).
I've verified that in both cases (at 125%), the "LogPixels" key in the registry is set to 120 dpi. So some Windows API is reporting this incorrectly (big surprise there); maybe pegging the dpi to one of the three pre-determined settings.
High DPI is still a hot mess in WIndows - Microsoft's own apps don't work properly (no plans to improve SQL server), and large devs like Adobe are still dealing with it. I myself will be testing some MFC apps I'm maintaining on 4k display and dread the results.
In any case this particular problem seems unique to a lot of audio apps (I haven't ported much to my new PC to test yet but Ableton and Renoise exhibit the same problem), I'm curious if anyone else has found a workaround.
(In Adobe's case, getting InDesign Creative Cloud to properly display cursors that aren't the size of gorilla hands entails setting an environment variable! I'm having flashbacks to editing config.sys and autoexec.bat files in DOS - seriously?)
It's still 1981 in Redmond...