A few users using the Windows 10 Insider Preview have found that after a certain point in the Prerelease builds, starting at 14915 it seems, the Unreal Editor and Epic Games Launcher context menus have stopped displaying correctly.

Regression?: No
This is not editor version specific and only depends on being on one of these prerelease builds.

A user mentioned that this does not happen when running the editor with OpenGL. Another user found a line of code that can be changed to fix the issue, although I cannot say that this wouldn't break other things.

Inside of: Engine\Source\Runtime\Core\Private\Windows\WindowsWindow.cpp
Commenting out this line fixes the issue:

WindowExStyle |= WS_EX_COMPOSITED;
Steps to Reproduce
  1. Using a computer that has Windows 10 Pro Insider Preview Build 14936.rs_prerelease.160923-1700, launch the Epic Games Launcher or Unreal Editor
  2. Click any option in the editor that would cause a dropdown menu to appear
    Result: With most dropdown menus, the menu will not appear or will only appear after moving your cursor.
    Expected: The menus should appear every time.

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ComponentUE - Editor - UI Systems - Slate
Affects Versions4.
Target Fix4.14
Fix Commit3156617
Main Commit3168049
Release Commit3167492
CreatedOct 3, 2016
ResolvedOct 10, 2016
UpdatedMay 2, 2018