TreeViewItem doesn't update IsSelected in SelectionMode=Multiple when clicking on Checkbox or content

Describe the bug When you have a TreeView using ItemsSource binding and set to SelectionMode="Multiple", the IsSelected property is not changed when clicking on the checkbox. Also, the checkbox is not changed when clicking on the item, either.

Steps to reproduce the bug

Steps to reproduce the behavior:

1. Clone XamlControlsGallery and update Microsoft.UI.Xaml to latest stable release (v2.0.181018003.1)
2. Go to TreeViewPage.xaml under ControlPages.
3. Go to third TreeView sample (A TreeView with DataBinding Using ItemSource)
4. Add SelectionMode="Multiple" to TreeView
5. Add IsSelected="{x:Bind IsSelected,Mode=TwoWay}" to the TreeViewItem
6. Add Debug.WriteLine($"Selected changed: {value}"); to the set statement for IsSelected in the code-behind file. Include using statement for Debug.
7. Run sample, go to TreeView page, and try clicking on the checkboxes, then the item contents instead.

Expected behavior The debug output should show Selected changed: true when the checkbox is checked and Selected changed: false when unchecked. Also, the checkbox should be checked/unchecked when the content of the TreeViewItem is toggled.

Screenshots

Version Info

NuGet package version: Microsoft.UI.Xaml v2.0.181018003.1

Windows 10 version:

• Insider Build (1809)
• October 2018 Update (17763)
• April 2018 Update (17134)
• Fall Creators Update (16299)
• Creators Update (15063)
• Anniversary Update (14393)

Device form factor:

• Desktop
• Mobile
• Xbox
• Surface Hub
• IoT

Additional context

[MrDeej]

This is still a issue 17.02.2022. Please fix!

[lukedukeus]

How is this still an issue after four years? please fix it.