https://bugs.kde.org/show_bug.cgi?id=522547

--- Comment #5 from giors <[email protected]> ---
Created attachment 193985
  --> https://bugs.kde.org/attachment.cgi?id=193985&action=edit
Reproduced with KWin's **native blur effect** (Better Blur DX unloaded via DBus
before the session), so this is not caused by third-party effects.



Environment: Plasma 6.7.2 (Wayland), kwindowsystem 6.27.0, plasma-integration
6.7.2, qt6-wayland 6.11.1, LibreOffice 26.2.4 with the kf6 VCL plugin. Full
client-side WAYLAND_DEBUG=1 trace attached (zstd-compressed; wl_keyboard.key
keycodes replaced with REDACTED for privacy, timings and press/release states
preserved); the trigger is Writer's word-completion tooltip
appearing/disappearing while typing.

The trace shows this is **not a tight race but reuse of a stale
ext_background_effect_surface_v1 by the client-side integration**:

```
[1260610.208] -> wl_compositor#4.create_surface(new id wl_surface#87)      #
tooltip surface
[1326084.822] -> ext_background_effect_manager_v1#81.get_background_effect(new
id ext_background_effect_surface_v1#73, wl_surface#87)
[1326084.827] -> ext_background_effect_surface_v1#73.set_blur_region(nil)
[1364087.641] -> wl_surface#87.destroy()                                   #
tooltip hidden; #73 is NEVER destroyed
[1366670.862] ->
ext_background_effect_surface_v1#73.set_blur_region(wl_region#94)   # 2.6 s
later
[1366671.416] wl_display#1.error(ext_background_effect_surface_v1#73, 0, "tried
to set blur region on destroyed surface")
```

Note the 2.6 seconds between the surface destruction and the fatal request.
In between, several other tooltip surfaces were created and each correctly got
a *fresh* effect object via get_background_effect; only this stale #73 was
reused for a blur-region update without a new get_background_effect. So the
client-side blur bookkeeping (KWindowSystem / plasma-integration for Qt
windows?) keeps the effect object alive across the native surface teardown and
later writes through it, and KWin's (spec-compliant) fatal error takes down
the whole application — LibreOffice exits instantly with no coredump.

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