WPF/XPS font handling error that still worked a few week ago

[jbe2277]

Description

I have an automated UI test executed on GitHub's Windows Server 2022 runner.

• It was working until Jul 27, 2026: https://github.com/jbe2277/waf/actions/runs/30286284736
  • OS: Microsoft Windows NT 10.0.20348.0; .NET: 10.0.10
• Now Aug 12, 2026 it started failing with always the same error: https://github.com/jbe2277/waf/actions/runs/31636504949
  • OS: Microsoft Windows NT 10.0.20348.0; .NET: 10.0.11

Context:

• .NET 10 / WPF 10 application
• Open source: Writer sample application - https://github.com/jbe2277/waf
• Error comes when it creates a FixedDocument for print preview

Reproduction Steps

• Run the UI test action (GitHub) on GitHub's Windows Server 2022 runner.
• The error occurs on my Windows 11 PC as well - but only after I updated .NET 10.0.10 to 10.0.11.

Steps:

• Open System.Waf.slnx solution file (https://github.com/jbe2277/waf/tree/master/src/System.Waf)
• Writer.Presentation > Set as Startup Project
• Start application
• Press New
• Enter Hello
• Menu > Print preview
• Exception: System.Windows.Markup.XamlParseException

Expected behavior

UI test should work

Actual behavior

Application shows the error:

2026-08-12 20:17:18.47 [I] 7948 App Waf Writer 8.0.0.0 is starting; OS: Microsoft Windows NT 10.0.20348.0; .NET: 10.0.11 
2026-08-12 20:17:24.45 [E] 7948 Writer.P UnhandledException; IsTerminating=True System.Windows.Markup.XamlParseException: 'Initialization of 'System.Windows.Documents.FixedDocument' threw an exception.' Line number '1' and line position '105'.
 ---> System.FormatException: One of the identified items was in an invalid format.
   at System.Runtime.InteropServices.Marshal.ThrowExceptionForHR(Int32 errorCode, IntPtr errorInfo)
   at MS.Internal.Text.TextInterface.Factory.CreateFontFace(Uri filePathUri, UInt32 faceIndex, FontSimulations fontSimulationFlags)
   at System.Windows.Media.GlyphTypeface.Initialize(Uri typefaceSource, StyleSimulations styleSimulations)
   at System.Windows.Documents.Glyphs.ParseGlyphRunProperties()
   at System.Windows.Documents.Glyphs.ComputeMeasurementGlyphRunAndOrigin()
   at System.Windows.Documents.Glyphs.MeasureOverride(Size constraint)
   at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
   at System.Windows.UIElement.Measure(Size availableSize)
   at System.Windows.Controls.Canvas.MeasureOverride(Size constraint)
   at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
   at System.Windows.UIElement.Measure(Size availableSize)
   at System.Windows.Documents.FixedPage.MeasureOverride(Size constraint)
   at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
   at System.Windows.UIElement.Measure(Size availableSize)
   at System.Windows.Documents.FixedDocument.GetPage(Int32 pageNumber)
   at System.Windows.Documents.FixedDocument.OnInitialized(Object sender, EventArgs e)
   at MS.Internal.Xaml.Runtime.ClrObjectRuntime.InitializationGuard(XamlType xamlType, Object obj, Boolean begin)
   --- End of inner exception stack trace ---
   at System.Windows.Markup.XamlReader.RewrapException(Exception e, IXamlLineInfo lineInfo, Uri baseUri)
   at System.Windows.Markup.WpfXamlLoader.Load(XamlReader xamlReader, IXamlObjectWriterFactory writerFactory, Boolean skipJournaledProperties, Object rootObject, XamlObjectWriterSettings settings, Uri baseUri)
   at System.Windows.Markup.WpfXamlLoader.Load(XamlReader xamlReader, Boolean skipJournaledProperties, Uri baseUri)
   at System.Windows.Markup.XamlReader.Load(XamlReader xamlReader, ParserContext parserContext)
   at System.Windows.Markup.XamlReader.Load(XmlReader reader, ParserContext parserContext, XamlParseMode parseMode, Boolean useRestrictiveXamlReader, List`1 safeTypes)
   at System.Windows.Markup.XamlReader.Load(Stream stream, ParserContext parserContext, Boolean useRestrictiveXamlReader)
   at System.Windows.Xps.Packaging.XpsDocument.GetFixedDocumentSequence()
   at Waf.Writer.Presentation.Views.PrintPreviewView.LoadedHandler(Object sender, RoutedEventArgs e) in D:\a\waf\waf\src\System.Waf\Samples\Writer\Writer.Presentation\Views\PrintPreviewView.xaml.cs:line 49
   at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
   at System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args)
   at System.Windows.BroadcastEventHelper.BroadcastEvent(DependencyObject root, RoutedEvent routedEvent)
   at System.Windows.BroadcastEventHelper.BroadcastLoadedEvent(Object root)
   at System.Windows.Media.MediaContext.FireLoadedPendingCallbacks()
   at System.Windows.Media.MediaContext.FireInvokeOnRenderCallbacks()
   at System.Windows.Media.MediaContext.RenderMessageHandlerCore(Object resizedCompositionTarget)
   at System.Windows.Media.MediaContext.RenderMessageHandler(Object resizedCompositionTarget)
   at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
   at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Int32 numArgs, Delegate catchHandler)
   at System.Windows.Threading.DispatcherOperation.InvokeImpl()
   at MS.Internal.CulturePreservingExecutionContext.CallbackWrapper(Object obj)
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state)
--- End of stack trace from previous location ---
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state)
   at MS.Internal.CulturePreservingExecutionContext.Run(CulturePreservingExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Windows.Threading.DispatcherOperation.Invoke()
   at System.Windows.Threading.Dispatcher.ProcessQueue()
   at System.Windows.Threading.Dispatcher.WndProcHook(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
   at MS.Win32.HwndWrapper.WndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
   at MS.Win32.HwndSubclass.DispatcherCallbackOperation(Object o)
   at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
   at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Int32 numArgs, Delegate catchHandler)
   at System.Windows.Threading.Dispatcher.LegacyInvokeImpl(DispatcherPriority priority, TimeSpan timeout, Delegate method, Object args, Int32 numArgs)
   at MS.Win32.HwndSubclass.SubclassWndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam)
   at MS.Win32.UnsafeNativeMethods.DispatchMessage(MSG& msg)
   at System.Windows.Threading.Dispatcher.PushFrameImpl(DispatcherFrame frame)
   at System.Windows.Application.RunDispatcher(Object ignore)
   at System.Windows.Application.RunInternal(Window window)
   at Waf.Writer.Presentation.App.Main() System.Object: 

Regression?

Yes, looks like a regression issue

• worked with 10.0.10
• started failing with 10.0.11

Known Workarounds

No response

Impact

No response

Configuration

No response

Other information

No response