ListBox with Extended SelectionMode "remembers" start of previous selection range separated by single item selection

[clemarescx]

To Reproduce
Steps to reproduce the behavior in the Showcase project:

1. Go to ListBox > Bound (the default view when starting the project)
2. In the LeftBoundListBox, select item 2
3. Hold shift, and select item 10
   • Range 2 to 10 is selected, as expected
4. Select a single item within the previous range by clicking without holding shift, e.g item 5
   • Only item 5 is selected, as expected
5. Hold shift and click an item with index higher than previously selected item, e.g item 7
   • Range 2 to 7 is selected, which wasn't expected

Note: this does not occur when setting dd:DragDrop.DragSourceIgnore="True" on the ListBox.

Expected behavior
Only the items in the selected range should be selected.

Findings
A similar issue occurs "backwards":

1. select item 10 first
2. hold shift and select item 2
3. select a single item 7
4. hold shift and select item 5
   • range 10 to 5 will be selected

SelectionChanged event is raised multiple times when going from selected range to single selection

• When selecting the single item between the two range selections, the SelectionChanged event on the ListBox is raised multiple times, each time removing a single item from SelectedItems, until only the single item is selected.
• To view this, add the following handler to LeftBoundListBox:
  ListBoxSamples.xaml:

   <ListBox x:Name="LeftBoundListBox"
             ...
             SelectionChanged="LeftBoundListBox_OnSelectionChanged" />

  ListBoxSamples.xaml.cs:

  private void LeftBoundListBox_OnSelectionChanged(object sender, SelectionChangedEventArgs e)
  {
      var selectedItems = this.LeftBoundListBox.SelectedItems.OfType<ItemModel>().ToList();
      var itemIndices = selectedItems.Select(svm => $"{svm.Index}");
      var indexList = string.Join(", ", itemIndices);
      Debug.WriteLine($"selected: : {indexList}");
  }

  When running the same sequence as described in To reproduce, the expected output will be:

  selected: : 2
  selected: : 2, 3, 4, 5, 6, 7, 8, 9, 10
  selected: : 3, 4, 5, 6, 7, 8, 9, 10
  selected: : 4, 5, 6, 7, 8, 9, 10
  selected: : 5, 6, 7, 8, 9, 10
  selected: : 5, 7, 8, 9, 10
  selected: : 5, 8, 9, 10
  selected: : 5, 9, 10
  selected: : 5, 10
  selected: : 5
  selected: : 5, 2, 3, 4, 6, 7
  

Demo of the sequence

Desktop (please complete the following information):

• OS: Microsoft Windows 10 Pro
• Version 10.0.19043 Build 19043

Additional context
Tested with VS 2019 and VS 2022 Preview 4.1:

• .NET Framework 4.5
• .NET Framework 4.6.2