title: Property change is not propagated to binding target (UWP)
body: <p>I have a ViewModel and a Class. They look like this:</p>
  
  <pre><code>//viewmodel
  public class MyViewModel : ViewModelBase {
  
      private MyClass myClass;
      public MyClass MyClass{
          get{
              return myClass;
          }
          set{
              this.myClass = value;
              base.OnPropertyChanged();
          }
      }
  
      private string testString;
      public string TestString{
                  get{
              return testString;
          }
          set{
              this.testString = value;
              base.OnPropertyChanged();
          }
      }
  
      public MyViewModel(){
          this.MyClass = new MyClass();
          this.TestString = "blah, blah, blah"
      }}
  
  
  
  //class
      public class MyClass : ViewModelBase{
      private string  myString;
      public string MyString{
          get {
          return myString
          }
          set{
              this.myString = value;
              base.OnPropertyChanged();
          }
      }
  
      public MyClass (){
          this.MyString = "25";   }}
  </code></pre>
  
  <p>The base class - ViewModelBase implements INotifyChange and contains OnPropertyChanged handler logic. 
  I have a UserControl where I wish to bind values from MyClass like this:</p>
  
  <pre><code>  &lt;TextBlock Text="{x:Bind  Path=MyViewModel.MyClass.MyString, Mode=TwoWay}"&gt;&lt;/TextBlock&gt;
  </code></pre>
  
  <p>However this does not work. Value is binded in initialisation correctly, but any change in MyViewModel.MyClass.MyString is not reflected in texblock, the text remains the same. The OnPropertyChange is raised, the breakpoint in ViewModelBase is hit with MyString value changed, but it is somehow not propagated to texblock.
  Binding on simple value from MyClass works like charm, this textblock is updated, when property is changed:</p>
  
  <pre><code>  &lt;TextBlock Text="{x:Bind  Path=MyViewModel.TestString, Mode=TwoWay}"&gt;&lt;/TextBlock&gt;
  </code></pre>
  
  <p>What am I missing? Why the textblock with binding to "MyViewModel.MyClass.MyString" is not being updated?</p>