Windows 10, version 1803

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Current status as of November 12, 2019:       
Windows 10, version 1803 (the April 2018 Update) Home and Pro editions have reached end of service. For Windows 10 devices that are at, or within several months of reaching end of service, Windows Update will automatically initiate a feature update (with users having the ability to choose a convenient time); keeping those devices supported and receiving the monthly updates that are critical to device security and ecosystem health.
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Known issues

This table offers a summary of current active issues and those issues that have been resolved in the last 30 days.

SummaryOriginating updateStatusLast updated
Windows Presentation Foundation (WPF) apps might close, or you may receive an error
Microsoft and third-party applications which use the .Net UI framework called WPF might have issues.
OS Build 17134.2026
KB4601354
2021-02-09
Mitigated
2021-02-11
20:41 PT

Issue details

February 2021

Windows Presentation Foundation (WPF) apps might close, or you may receive an error

StatusOriginating updateHistory
MitigatedOS Build 17134.2026
KB4601354
2021-02-09
Last updated: 2021-02-11, 08:41 PT
Opened: 2021-02-11, 05:49 PT
After installing KB4601354, Windows Presentation Foundation (WPF) apps might close, or you may receive an error similar to:
        Exception Info: System.NullReferenceException at System.Windows.Interop.HwndMouseInputProvider.HasCustomChrome(System.Windows.Interop.HwndSource, RECT ByRef)
        at System.Windows.Interop.HwndMouseInputProvider.GetEffectiveClientRect(IntPtr)
        at System.Windows.Interop.HwndMouseInputProvider.PossiblyDeactivate(IntPtr, Boolean)
        at System.Windows.Interop.HwndMouseInputProvider.Dispose()
 
This occurs when disposing an HwndSource whose RootVisual is null, a situation that arises in Visual Studio when docking or splitting windows, and could arise in other apps.

Affected platforms:
  • Client: Windows 10, version 1803; Windows 10 Enterprise LTSC 2016; Windows 10, version 1607
  • Server: Windows Server, version 1803; Windows Server 2016
Workaround: To mitigate this issue when using Microsoft Visual Studio, update to the latest version. This issue is resolved starting with the following releases:
Developers can mitigate this issue in their own apps by setting two AppContext switches using one of the methods described in AppContext Class (System) under the heading “AppContext for library consumers”. The switches are named Switch.System.Windows.Interop.MouseInput.OptOutOfMoveToChromedWindowFix and Switch.System.Windows.Interop.MouseInput.DoNotOptOutOfMoveToChromedWindowFix; both should be set to “true”. The first switch avoids the crash, but re-introduces the issue addressed in this update. The second switch is currently ignored, but will be recognized in a future .NET update that addresses the issue for the null-reference crash; it restores the behavior originally intended to be addressed in this update.

For example, using the app.config file method to apply the workaround at application scope:
        <AppContextSwitchOverrides value="Switch.System.Windows.Interop.MouseInput.OptOutOfMoveToChromedWindowFix=true; Switch.System.Windows.Interop.MouseInput.DoNotOptOutOfMoveToChromedWindowFix=true " />

Next steps: We are working on a resolution and will provide an update in an upcoming release.