Microsoft confirms KB5120998 resets Windows 11 desktop settings

Microsoft has confirmed that KB5120998 stops some Windows desktop settings from loading. On affected machines the custom wallpaper is replaced by a solid black background. The confirmation went up on the Windows release health dashboard on 2 September 2026, roughly a week after the update shipped.

KB5120998 is the optional, non-security preview update for Windows 11 released on 27 August 2026. It takes version 25H2 to build 26200.9278 and version 24H2 to build 26100.9278, and it carries the taskbar position, Start menu and search changes that are due to reach everyone in a later cumulative update.

Per Microsoft's release health entry, the fault is not limited to the wallpaper. Slideshow settings and contrast themes may fail to load in the same way.

The settings are not being overwritten with a black image. They are failing to load. Microsoft describes a load path that breaks regardless of the value stored, so Windows falls back to a default black background instead.

That detail explains the behaviour users kept reporting. You can open Settings, go to Personalization and pick your image again, and it may look fixed. The same load failure returns on the next sign-in or restart. Microsoft states directly that attempting to manually restore customized settings does not work on affected devices.

It is the same shape of failure described in the mouse bug from the same update: a settings read that fails, and a default that wins.

Microsoft lists Windows 11 version 25H2 and Windows 11 version 24H2 as the affected clients. No Windows Server release is listed. The trigger is installing KB5120998 or any Windows update released after it.

Beyond that, the affected population is not defined. Microsoft has not published a device count, and it has not named a locale, a graphics configuration, a display scaling setting or a hardware family that predicts the failure. The word Microsoft uses is "some" devices, so treat exposure across a fleet as unpredictable until the entry is updated.

KB5120998 already carried a confirmed known issue against mouse personalization. Microsoft opened that entry on 28 August 2026 and moved it to Confirmed on 1 September, describing cursors and cursor animations reverting to standard settings.

The cause there is stated. Per Microsoft's release health entry, the mouse bug is caused by code components used in non-English Windows installations, where the settings fail to load and a default is used instead. Manual restore fails for the same reason as the desktop issue.

The two entries read almost identically, which is worth noting for anyone triaging both at once. Microsoft has not said the two bugs share a root cause.

For an MSP or an internal IT team the cost here is support load, not downtime. A black desktop on a domain-joined machine looks like a broken profile, a failed policy or a licensing problem, so it pulls technicians into the wrong investigation before anyone checks the installed update list.

Contrast themes are the part worth escalating. Those are accessibility settings, and a user who depends on one loses it with no way to put it back. That moves the issue past cosmetic for a small group of people.

There is no security exposure. KB5120998 carries no security fixes, so declining it leaves nothing unpatched.

Microsoft has published no workaround, so the options are to hold the update and to handle the machines that already took it.

Keep KB5120998 out of broad deployment. It is optional, which means it normally waits behind a Download and install click in Windows Update. The exception matters in unmanaged and lightly managed estates: devices with "Get the latest updates as soon as they're available" turned on will pull it automatically. Check that toggle in your build baseline, and confirm that your patching tool is not approving preview updates.

For machines already affected, several outlets that tested the earlier reports, including Windows Latest and 4sysops, found that removing KB5120998 restored normal wallpaper behaviour. That is a third-party finding rather than Microsoft guidance, and uninstalling also takes back the taskbar, Start menu and search changes the update introduced.

Microsoft says it is working on a resolution for a future Windows update and has given no date. The next scheduled cumulative update is Microsoft's September 2026 security release, which is the first realistic checkpoint, though nothing in the known issue entry promises the fix arrives with it.

Two things are worth tracking on the release health pages. The first is whether the desktop entry ever picks up a stated cause the way the mouse entry did, since that would tell you which devices to expect trouble on. The second is the delivery method: a Known Issue Rollback would reach unmanaged devices quickly, while a fix folded into a cumulative update lands on your normal patch cycle.

Affected Windows 11 devices lose their desktop wallpaper to a solid black background, and may also lose slideshow settings and contrast themes, with no way for the user to restore them until Microsoft ships a fix.

Security: None. KB5120998 is a non-security preview update.

Microsoft has confirmed that KB5120998 stops some Windows 11 desktop settings from loading, leaving a black background, and possibly taking slideshow settings and contrast themes with it.