title: MSbuild 4 with /pp (/preprocess) does not write preprocessed file
body: <p>I want to create a pre processed file with msbuild for diagnostic reasons. The documentation states, that I just need to call msbuild with the /pp:Filename switch. So I did:</p>
  
  <pre><code>msbuild project.sln /t:Build /p:Configuration=Release /pp:out.txt
  </code></pre>
  
  <p>It also creates an 'out.txt' file, so the argument obviously has SOME impact, but the file is empty (size 0, no content). So what could be possible reasons the preprocessed project file isn't written correctly? The project file builds fine though.</p>