Wpf DataGrid SelectedItem在单元格编辑后失去绑定

我有一个DataGrid绑定到一个项目集合(规则)。如果我在DataGrid中手动编辑其中一个项目，似乎网格上的SelectedItem绑定停止工作(控制器中的RuleListViewModelPropertyChanged再也不会被调用)。但只有当我实际改变单元格中项目的值时，否则SelectedItem保持正常工作。

我已经剥离了一些不相关的东西，所以这基本上是我所拥有的。首先，我有以下DataGrid:

<DataGrid x:Name="RuleTable" Grid.Row="1" Grid.ColumnSpan="2" ItemsSource="{Binding Rules}" SelectedItem="{Binding SelectedRule, Mode=TwoWay}" 
               BorderThickness="0" >
        <DataGrid.Columns>
            <DataGridTextColumn Binding="{Binding TargetValue, UpdateSourceTrigger=PropertyChanged, ValidatesOnDataErrors=True, 
                                  ValidatesOnExceptions=True, NotifyOnValidationError=True}" 
                                Header="{x:Static p:Resources.TargetValue}" Width="*" ElementStyle="{StaticResource TextCellElementStyle}"
                                EditingElementStyle="{StaticResource TextCellEditingStyle}"/>
        </DataGrid.Columns>
    </DataGrid>

与ViewModel看起来像这样:

public class RuleListViewModel : ViewModel<IRuleListView>
{
    private IEnumerable<Rule> rules;
    private Rule selectedRule;
    public RuleListViewModel(IRuleListView view)
        : base(view)
    {
    }
    public RuleListViewModel() : base(null) {}
    public IEnumerable<Rule> Rules
    {
        get
        {
            return rules;
        }
        set
        {
            if (rules != value)
            {
                rules = value;
                RaisePropertyChanged("Rules");
            }
        }
    }
    public Rule SelectedRule
    {
        get
        {
            return selectedRule;
        }
        set
        {
            if (selectedRule != value)
            {
                selectedRule = value;
                RaisePropertyChanged("SelectedRule");
            }
        }
    }
}

最后一个Controller看起来像这样:

public class RuleController : Controller
{
    private readonly IShellService shellService;
    private readonly RuleListViewModel ruleListViewModel;
    private readonly DelegateCommand addRuleCommand;
    private readonly DelegateCommand deleteRuleCommand;
    [ImportingConstructor]
    public RuleController(IShellService shellService, IEntityService entityService, RuleListViewModel ruleListViewModel)
    {
        this.shellService = shellService;
        this.ruleListViewModel = ruleListViewModel;
    }
    public void Initialize()
    {
        AddWeakEventListener(ruleListViewModel, RuleListViewModelPropertyChanged);
        shellService.RuleListView = ruleListViewModel.View;
        List<Rule> rules = GetRules();
        ruleListViewModel.Rules = new ObservableCollection<Rule>(rules);
    }
    private void RuleListViewModelPropertyChanged(object sender, PropertyChangedEventArgs e)
    {
        if (e.PropertyName == "SelectedRule")
        {
            // This never gets called after edit
        }
    }
}

我真的不知道问题是什么，但是因为我实际上必须改变值来体验这种行为(只在单元格中单击而不编辑任何东西都可以正常工作)，我猜它与SelectedItem绑定中断有关，当我改变绑定到它的项目的值时?!