I didn't have access to a 16:9 monitor for a while and temporarily had to use a 5:4 one attached to the motherboard with that set as graphics priority in the BIOS. After switching back to my GPU on my new 16:9 one, 4:3/5:4 games like Cave Story and Yume Nikki get stretched in fullscreen instead of having black bars on the sides, which never happened before this. I know it's not this monitor because I also tested it with my old 16:9 monitor where the same thing happened. I have an Nvidia GPU and an Azrock motherboard.