title: LaunchMode "singleTop" is ignored when activity is started with startActivityForResult
body: <p>I launch an activity with <code>startActivityForResult()</code> and want to prevent multiple instances from being started at the top of activity stack. So I expect <code>android:launchMode="singleTop"</code> to do its work, but for some reason the flag gets ignored. </p>
  
  <p>After some investigations I managed to launch only one instance by adding <code>FLAG_ACTIVITY_REORDER_TO_FRONT</code> to intent, but I would be grateful if someone could explain me the reason why "singleTop" doesn't work in such case. The code is very simple.</p>
  
  <pre><code>// Activity class
  Intent intent = new Intent(this, DetailsActivity.class);
  // multiple instances can be launched without this line
  intent.setFlags(Intent.FLAG_ACTIVITY_REORDER_TO_FRONT); 
  startActivityForResult(intent, REQUEST_CODE_DETAILS);
  
  // AndroidManifest.xml
  &lt;activity
      android:name=".DetailsActivity"
      android:launchMode="singleTop"/&gt;
  </code></pre>