Have you tried Custom Resolutions?
Not sure that would help, but ever try it?
Why use 'center' ? Try using full screen and adjust your resolution to 1920x1080
I confirm! GPU Scaling is bugged in 17.7.2.
I revert back to 16.12.x and GPU Scaling is working properly. There's one exception, 1280x720 is always scaled to fullscreen even if we set center.
I will try with 17.7.1 later and edit this post.