title: preprocessor fails to reflect project settings in visual studio
body: <p>For some reason I've set a preprocessor variable, but it doesn't reflect in the build.</p>
  
  <p>Here is the project build setting:</p>
  
  <p><img src="https://i.stack.imgur.com/VFly8.png" alt="project build setting"></p>
  
  <p>The desired path is grayed out:</p>
  
  <p><img src="https://i.stack.imgur.com/I3jkM.png" alt="namespace reference"></p>
  
  <p>This is not just a cosmetic problem. It won't build:</p>
  
  <p><img src="https://i.stack.imgur.com/2rE6r.png" alt="enter image description here"></p>
  
  <p><strong>EDIT</strong>: Sometimes when I close/reload the project the variable is gone, but I always see it in the project file when I edit it:</p>
  
  <pre><code>&lt;DefineConstants&gt;TRACE;DEBUG;MISMO32&lt;/DefineConstants&gt;
  </code></pre>