ModalTest - Windows App SDK Bug Reproduction

This is a minimal C++/WinRT application that has hello world win32 app and modal app using desktopChildSitebridge.

Reproduction Steps For crash with Modal dangling ref issue

1. Build and run ModalTest.cpp
2. Click "Show Modal" button
3. Click the "X" button on the modal to close it
4. Click anywhere on the parent window
5. Application crashes with FailFast in contentappwindowbridge.cpp(835)

Architecture

• Parent Window: Win32 HWND with DesktopChildSiteBridge connected to ContentIsland
• Modal Window: DesktopPopupSiteBridge with parent island as parent
• Cleanup Sequence: Hide → Close popup → Close island → nullptr

Key Files

• ModalTest.cpp - Main test application demonstrating the bug
• DesktopAppWin32.vcxproj - Visual Studio project file

Build Requirements

• Visual Studio 2022 or later
• Windows App SDK 1.7 or later
• C++/WinRT support
• Windows 10 SDK (10.0.19041.0 or later)

Expected vs Actual Behavior

Expected

Modal closes cleanly, parent window remains fully functional.

Actual

Modal closes successfully, but clicking parent window crashes with:

contentappwindowbridge.cpp(835)\Microsoft.UI.Input.dll!00007FF8BC10BFD5: 
FailFast(1) tid(9e90) 8000FFFF Catastrophic failure