title: strange Problem with WPF Textbox stringformat - Cursor moves back
body: <p>I am using WPF 4.0 TextBox and binding. I am using StringFormat to format the number as currency. the XAML looks like this:</p>
  
  <pre><code>&lt;TextBox Text="{Binding Path=ValueProperty, ValidatesOnDataErrors=True, ValidatesOnExceptions=True, StringFormat={}{0:C}, UpdateSourceTrigger=PropertyChanged}"&gt;
  &lt;/TextBox&gt;
  </code></pre>
  
  <p>Everything seems to work correctly except for a strange behavior: 
  When for example a user types in 12: right after typing 1, the value in the textbox becomes $1.00 and the weird thing is the the cursor is moved to be between the $ and the 1. 
  So when a user simply types in 12, the result becomes $21.00.</p>
  
  <p>How can I fix this strange behavior?</p>