September 26, 2019 — KB4515871 Cumulative Update for .NET Framework 3.5 and 4.8 for Windows 10 version 1903 and Windows 10 version 1909

BCL¹

• Addresses an issue that affects thread contention that occurs in BinaryFormatter.GetTypeInformation by using ConcurrentDictionary to handle multi-thread access.

WPF²

• Addresses an issue that affects a WPF ComboBox (or any Selector) within a DataGrid cell that can try to change its selection properties (SelectedIndex, SelectedItem, SelectedValue) when the cell's data item is re-virtualized or removed from the underlying collection. This can occur if the Selector's ItemSource property is data bound through the cell's DataContext setting. Depending on the virtualization mode and the bindings that are declared for the selection properties, the symptoms can include unexpected changes (to null) of the data item's properties, and unexpected displays (as null) of other data items that re-use the UI that was previously attached to the revirtualized item.

• Addresses an issue in which a WPF TextBox or RichTextBox element that has spell checking enabled crashes and returns an "ExecutionEngineException" error in some situations, including inserting text near a hyperlink.

• Addresses an issue that affects Per-Monitor Aware WPF applications that host System-Aware or Unaware child windows and that run on .NET Framework 4.8. This .NET version occasionally crashes and returns a "System.Collections.Generic.KeyNotFoundException" exception.

CLR³

• Addresses an issue that might cause handle leaks to occur in scenarios that repeatedly load and unload Mscoree.dll.

• Addresses rare cases that incorrectly cause process termination instead of delivering the expected NullReferenceException result.