Bug 491251

SUMMARY

I have 2 displays - a primary 4K @ 200% scaling (DisplayPort), and a secondary 1080p @ 100% scaling (HDMI), using Wayland.

When no apps are open, or all app windows on the primary display are minimized, opening a new app window from the Application Menu or KRunner results in the app window appearing on the secondary display, even though the mouse cursor was placed on the primary display during app launch, but only if the mouse cursor is not moved after opening the app. If you move the mouse cursor immediately after clicking the app, it will launch on the correct display. If an existing app is open and visible (not minimized) on the primary display, the app will launch on the correct display regardless of mouse cursor movement. Launching apps from the panel Task Manager shows correct behavior regardless of mouse cursor movement or existing visible app windows.

Even entering "Edit mode" by right-clicking the desktop, and clicking "Display Configuration" for example, without moving the mouse (keep it dead-still) results in the window opening on the incorrect (secondary) display.

STEPS TO REPRODUCE
1. Set up 2 monitors, one primary at 200% scaling and one secondary at 100% scaling.
2. Close all app windows.
3. On the primary 200% scaling display, use the Application Menu or KRunner to launch an app such as Dolphin or Konsole, but do not move the mouse after clicking (hold the mouse dead-still during/after the click).
4. Observe the app window opening on the incorrect display.
5. Close all app windows and try launching again, but this time move the mouse cursor constantly just after clicking.
6. Observe the app window opening on the correct display (the one the mouse cursor is moving around on).

SOFTWARE/OS VERSIONS
Linux: 6.10.2-arch1-2 Arch Linux (up-to-date as of August 4, 2024)
KDE Plasma Version: 6.1.3 (Arch package plasma-desktop 6.1.3-1)
Qt Version: 6.7.2 (Arch package qt6-wayland 6.7.2-4)

ADDITIONAL INFORMATION

I am using an AMD Radeon R9 390X (Hawaii) GPU with amdgpu driver, Mesa, RADV Vulkan. The secondary display is configured to be to the left of the primary display. XWayland apps are set to "Apply scaling themselves".

There is another multi-monitor bug that affects some apps (such as LibreOffice), with LibreOffice using incorrect scaling depending on the order of monitor wake-up/connection (it will use the scaling value from the first connected display regardless of Plasma/KScreen settings, only replugging monitors in the correct order resolves the issue). But I assume this should be a separate bug report from this one, as I am not sure if they are related.