Gamescope integer scaling leads to windowed mode

When I use gamescope with a smaller-than-native resolution and integer scaling, afaik it should look like the left image. However, I get a window like on the right without black background. These are my launch parameters: gamescope -w 1920 -h 1080 -W 3440 -H 1440 -S integer Using fullscreen (-f) or borderless fullscreen (-b) don't seem to make any difference. I'm on AMD.