Start11 triggers spontaneous Task View overlay on Windows 11 25H2 build 26200.9278 (KB5120998)
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Since installing the optional preview update KB5120998 (Windows 11 25H2, build 26200.9278) yesterday, the Task View overlay — the full-screen view showing open windows and virtual desktops — opens by itself, without any input from me. Setting the Start11 service to Manual startup and rebooting removes the problem completely.
System:- Windows 11 25H2, build 26200.9278 (KB5120998, installed 31 August 2026)
Symptom:
Task View opens roughly 200–300 ms after certain actions. The delay is consistent, and no key or mouse button is held at the time it appears. Pressing Esc closes it.
Reliable triggers:
- Pressing Win+R (overlay appears shortly after the Run dialog does)
- Closing the Run dialog with the X button
- Clicking an empty area of the desktop
- Clicking on the taskbar
The common factor appears to be an Explorer-owned window gaining or losing foreground focus.
Isolation:
- Set the Start11 service to Manual startup, rebooted
- All four triggers tested again: no Task View overlay at all
- Confirms the behaviour only occurs with Start11 running
Ruled out:
- Input devices. The overlay appears after the keys are released, with a consistent delay, so it is not a stuck Windows key or a stray HID report from peripherals.
- The known 25H2 Task View bug from the August cumulative (build 26200.9168). That was fixed in KB5120998, and I am on the build that contains the fix.
My assumption is that the taskbar rework in KB5120998 — movable taskbar, new sizing logic, Start menu changes — has broken compatibility with the Start11 taskbar hook. The most recent Start11 update I have is from July, which predates this Windows change.
Worth noting: these changes ship again in the mandatory September 8 security update, and Microsoft is rolling the features out gradually via feature flags. Other Start11 users on the same build may not be affected yet simply because the new taskbar code has not been enabled on their machine.