Why would setting game's screen resolution in GameUserSettings affect Editor's Application Scale?

One caveat is that the editor has not been extensively tested with non-1 DPI scales. You may find some bugs specific to the editor app. If you do, we’d love for you to report them so that we can get on fixing them.

If you aren’t finding any bugs at all, please let us know that as well. We’ll just make it persistent them. Until that time, you’re kind of an early adopter of the feature.