WPF 从代码更改 SelectedItem 后列表框错误突出显示

Question

I have a basic ListBox in my MVVM WPF project like this:

<ListBox ItemsSource="{Binding Models}" SelectedItem="{Binding SelectedModel, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" HorizontalContentAlignment="Stretch" >
  <ListBox.ItemTemplate>
    <DataTemplate>
      <Grid>
        <Grid.RowDefinitions>
          <RowDefinition/>
          <RowDefinition/>
        </Grid.RowDefinitions>
        <TextBlock Grid.Row="0" Text="{Binding Title}" FontWeight="SemiBold"/>
        <DockPanel Grid.Row="1" HorizontalAlignment="Stretch">
          <TextBlock Text="{Binding LastModified, StringFormat='{}{0:yyyy.MM.dd}'}" Margin="0,0,5,0" DockPanel.Dock="Left" FontSize="12"/>
          <TextBlock Text="{Binding Summary}" DockPanel.Dock="Right" HorizontalAlignment="Right" FontSize="12"/>
        </DockPanel>
      </Grid>
    </DataTemplate>
  </ListBox.ItemTemplate>
</ListBox>

In order to avoid the user to lose data when changing the SelectedItem without saving it, I modified the Setter of my SelectedModel like this:

 public MyModel SelectedModel
    {
      get { return _selectedModel; }
      set 
      {
        if (_selectedModel != null && _selectedModel.IsChanged)
        {
          var result = MessageBox.Show("Unsaved changes will be discarded when switching models. Save changes?", 
                                       "Unsaved Changes", MessageBoxButton.YesNoCancel);

          if (result == MessageBoxResult.Yes)
          {
            SaveModel(); //Saves and resets IsChanged
          }

          if (result != MessageBoxResult.Cancel)
          {
            _selectedModel = value;
          }    
        }
        else
        {
          _selectedModel = value;
        }
        OnPropertyChanged();
      }
    }

In my test case I have added 2 Items to my List (let's call them Item1 and Item2 ) I switch from Item1 to Item2 by clicking in the UI, but do not change the value of my Property bound to SelectedItem by pressing Cancel in the MessageBox . Thus, Item1 is still my SelectedItem , but Item2 is now highlighted blue.

How can I get my ListBox to update its highlighting, if its SelectedItem isn't actually the highlighted item?