Steps to reproduce:
1.Build the fullscreen example from this fork https://github.com/kaimast/glutin
2.Start the binary ./target/debug/examples/fullscreen
3. Press f to leave fullscreen
4. Press d to enable window decorations. Make sure they are enabled. I sometimes need to move the window around for them to appear
5. Press f to enter fullscreen again.

The result I get:
There is a gap at the bottom of the screen (about the height of the window decorations)

The expected result:
The window should fill the entire screen like in the beginning

System: Ubuntu 20.04 on Wayland
Screen: 4k resolution with 2x scale factor

Can move this issue to glutin, if you think it is not winit related...