title: Why tooltip doesn't update it's content when binding changes?
body: <p>I have written following xaml code:</p>
  
  <pre><code>&lt;Window x:Class="WpfApplication3.MainWindow"
          xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
          xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
          Title="MainWindow" Height="200" Width="200"&gt;
      &lt;StackPanel&gt;
          &lt;ListBox Name="listBox"&gt;
              &lt;ListBoxItem Content="item1" /&gt;
              &lt;ListBoxItem Content="item2" /&gt;
              &lt;ListBoxItem Content="item3" /&gt;
          &lt;/ListBox&gt;
  
          &lt;TextBlock DataContext="{Binding ElementName=listBox, Path=SelectedItem}" Text="{Binding Content}" ToolTip="{Binding Content}" /&gt;
  
          &lt;TextBlock DataContext="{Binding ElementName=listBox, Path=SelectedItem}" Text="{Binding Content}"&gt;
              &lt;TextBlock.ToolTip&gt;     
                  &lt;ToolTip Content="{Binding Content}"/&gt;              
              &lt;/TextBlock.ToolTip&gt;
          &lt;/TextBlock&gt;
      &lt;/StackPanel&gt;
  &lt;/Window&gt;
  </code></pre>
  
  <p>Why first tooltip always has the same text as it's parent <code>TextBlock</code> and second never changes it's content when I change selected item in <code>listBox</code>?</p>