title: WPF TextBox value doesn't change on OnPropertyChanged
body: <p>I have a TextBox whose Value is binded to a ViewModel property:</p>
  
  <pre><code>        &lt;TextBox Name="txtRunAfter" Grid.Column="4" Text="{Binding Mode=TwoWay, Path=RunAfter}" Style="{StaticResource TestStepTextBox}"/&gt;
  </code></pre>
  
  <p>The set and get were working fine until I tried to add some validation when the Value is set:</p>
  
  <pre><code>    private int _runAfter = 0;
      public string RunAfter
      {
          get
          {
              return _runAfter.ToString();
          }
  
          set
          {
              int val = int.Parse(value);
  
              if (_runAfter != val)
              {
                  if (val &lt; _order)
                      _runAfter = val;
                  else
                  {
                      _runAfter = 0;
                      OnPropertyChanged("RunAfter");
                  }
              }
          }
      }
  </code></pre>
  
  <p>Although the OnPropertyChanged is reached (I have dubugged that), the View is not changed.
  How can I make this work?</p>
  
  <p>Thanks,
  José Tavares</p>