Same. I'm on Adrenalin 18.2.2 and RX 460 2GB and have Virtual Super Resolution turned on + GPU scaling with preserve aspect ratio.
Native resolution of my monitor is 16:10 (1680x1050) when I try to use 16:9 (1920x1080) first frame rate gets locked to 30 fps or 30 Hz, and second, image is stretched instead of having black bars at top and bottom to keep aspect ratio.
I also have R7 260x and this works just fine on that card. It's something limited in software.
Please fix it Amd!