Help with graphic artefacts when restoring a window under Wayland

[Betterbird]

Hi,

I'm the Betterbird maintainer. Betterbird is a fork of Thunderbird.

Unlike Thunderbird, Betterbird can minimise to the system tray, which works fine 
on KDE and some other desktops (Gnome, Mate, Xfce) under X11.

Under Wayland, there is a problem described here:

https://github.com/Betterbird/thunderbird-patches/issues/399 or you might skip to
https://github.com/Betterbird/thunderbird-patches/issues/399#issuecomment-2640984080

It's not a KDE problem, the same happens under Gnome.

Minimise to the system tray works by hiding the application main window and 
displaying an icon in the system tray. When the icon is clicked, the application 
window is made visible again. Under the covers, that should be the 
`gtk_widget_show()` call. All this happens based on the Mozilla code base, so it's 
a little hard to dig through layers of Mozilla wrapper code.

The problem is that when the window is restored, it has a "phantom shadow" behind 
it and the controls to minimise/maximise/close or more the window are actually not 
where they are shown, but on the "phantom shadow" where they are not shown. 
Maximising the window and restoring it back to its size fixes the issue.

Our project has e-mail application programmers, not graphic (anomalies) 
programmers, so we're totally out of our depth.

KDE folks have helped before when we had issues with the system tray (for example 
here https://bugs.kde.org/show_bug.cgi?id=464264), so I'm hoping to get some help 
here.

Kind regards, Jörg.