I'm working on a WPF MVVM application and I've got a TextBox on my view that is bound to a DateTime property on the ViewModel. Seems simple enough, but when I clear the text in the TextBox, the property never changes. In fact, it never even fires until I begin typing "4/1..." and then it fires. What can I do to fix this? Obviously I could bind the TextBox to a string property and then update the real property in the setter, but that's a bit of a hack. There's got to be a better way...

ViewModel

private DateTime _startDate;
public DateTime StartDate
{
    get { return _startDate; }
    set
    {
        _startDate = value;
        OnPropertyChanged("StartDate");
    }
}

View

<TextBox Text="{Binding Path=StartDate, 
               UpdateSourceTrigger=PropertyChanged, 
               ValidatesOnDataErrors=true}"/>