ExtendsContentIntoTitleBar = true causes incorrect cursor events in child windows (WinAppSdk 1.6+)

[ramjke]

Describe the bug

This bug drives me mad. It started with WinAppSDK 1.6.

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

The bug is likely tied to how WinUI 3 manages input events when ExtendsContentIntoTitleBar is enabled. Which leads to a wide variety of bugs, such as controls flickering on hover.

Reproducible on: Windows App SDK 1.6.x
Not reproducible on: Windows App SDK 1.5.x

Steps to reproduce the bug

1. Enable ExtendsContentIntoTitleBar = true in the Main Window to use a modern title bar.
2. Create a Second Window.
3. Minimize the Main Window.
4. Hover over any controls in the Second Window.
5. Observe flickering and incorrect pointer events.

Repo to reproduce: https://github.com/ramjke/SecondWindowFlickeringTest

Expected behavior

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

Screenshots

video.mp4

NuGet package version

WinUI 3 - Windows App SDK 1.6.5: 1.6.250205002

Windows version

Windows 11 (23H2): Build 22631

Additional context

No response