title: .NET framework source stepping not working despite options set
body: <p>I have these options enabled, as shown in this screenshot:</p>
  
  <p><img src="https://i.imgur.com/OkELW.png" alt="screenshot"></p>
  
  <p>I also have the <code>System.Windows.Forms.dll</code> module selected:</p>
  
  <p><img src="https://i.stack.imgur.com/mw5zr.png" alt="screenshot"></p>
  
  <p>Yet it steps over the code. Specifically, I have this code in a subclass of <code>ListBox</code>:</p>
  
  <pre><code>protected override bool ProcessCmdKey(ref Message msg, Keys keyData)
  {
      return base.ProcessCmdKey(ref msg, keyData);
  }
  </code></pre>
  
  <p>I tried to set a breakpoint there and then step into this with F11, but it just steps over.</p>
  
  <p>What is missing to get this to work?</p>