I haven't fully figured this out yet but when I press a keyboard shortcut such as Ctrl+N in a Chrome window, I end up opening multiple windows if I'm not careful to press the key only very briefly. Something similar happens in Kolourpaint:
1.) open kolurpaint4
2.) double click a color in the palette and change a color there
3.) close kolourpaint window
-> it will wask for whether you want to save
4.) press Tab so the "Discard" button is focused (mnemonic Alt+D is unfortunately taken by Show desktop)
5.) Now hit return
It will suddenly popup a "Save Palette As" window, as by pressing return we accidentally confirmed the subsequent confirmation whether we want to save the custom palette to a file.

Another simpler way I just discovered is:
1.) start kwrite with platform xcb
2.) Press and hold Ctrl+N
-> you'll spawn a ton of new windows

If you do the same in kwrite with wayand, one single new window will appear and the shortcut won't trigger endlessly.

(Don't tell me this is yet again an Xwayland 1.18 issue :(