WinUI 3 Bug: ExtendsContentIntoTitleBar and Child Windows

This project demonstrates a bug in WinUI 3 where enabling ExtendsContentIntoTitleBar in the main window causes child windows to receive incorrect cursor signals.

🐛 Bug Description

When ExtendsContentIntoTitleBar = true; is set in the main window, and main window is minimized, child windows start incorrectly processing cursor events.

Video

video.mp4

Reproduction Steps

1. Run the app.
2. Click "Show Second Window" button.
3. Minimize the Main Window.
4. Hover over any controls in the Second Window.

Expected Behavior

• PointerEntered should trigger only once when the cursor enters a control.

Actual Behavior

• The debug console continuously logs "PointerEntered" messages while hovering.
• This can lead to flickering UI elements, such as ToggleSwitch.
• If the Main Window is visible (not minimized) or completely closed, everything works as expected.

🔍 Additional Notes

• The bug is likely tied to how WinUI 3 manages input events when ExtendsContentIntoTitleBar is enabled.
• A fix or workaround is currently unknown.

🛠 Environment

• OS: Windows 10/11
• Framework: WinUI 3
• Reproducible on: Latest Windows App SDK 1.6.4