title: When does the .csproj file get updated?
body: <p>I open my solution file in VS2010, right click on a project,  go to the build tab and switch the .NET framework from (say) 4 to 2.  Then I do a save all.  But my .csproj doesn't change - it still says </p>
  
  <pre><code>&lt;TargetFrameworkVersion&gt;v4.0&lt;/TargetFrameworkVersion&gt;
  </code></pre>
  
  <p>Why is this?  And what do I have to do to get this line to update? </p>