title: StringFormat shows error in Designer, but not after compiling
body: <p>I have a C#/WPF Programm with MVVM.</p>
  
  <p>Both <code>Kalkulation.Artikel.PartWeight</code> and <code>Kalkulation.Artikel.SprueWeight</code> are decimals. <br>The <strong>Format</strong> of both shall have one optional decimal place and a thousand seperator.</p>
  
  <p>I've implemented this like in the screenshot below.
  <a href="https://i.stack.imgur.com/s23LK.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/s23LK.png" alt="Error in StringFormat"></a></p>
  
  <p><em>For each <code>StringFormat</code> I get</em> <strong>three</strong> <em>errors:</em></p>
  
  <pre><code>Error   XLS0112 Expected ''.    Kalkulation MainWindow.xaml 113 
  Error   XLS0414 The type '' was not found. Verify that you are not missing an assembly reference and that all referenced assemblies have been built. Kalkulation    MainWindow.xaml 113 
  Error   XLS0112 Expected '
  </code></pre>
  
  <p>The picture shows the signs, that could not be displayed by Stackoverflow.
  <a href="https://i.stack.imgur.com/N1Xs9.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/N1Xs9.png" alt="enter image description here"></a></p>
  
  <p><br>
  <strong>When i compile, i have no Error at all, everything works as expected!</strong><br>
  The Errormessages pop up again, when i change something i the XAML Code.</p>
  
  <p>I have turned the Sync between Display an Textbox off to enter decimals with ease. <br><code>FrameworkCompatibilityPreferences.KeepTextBoxDisplaySynchronizedWithTextProperty = false;</code></p>
  
  <p>What can i do to change this? Can i at least "filter" the error messages?</p>