<p>There is no username popup suggesting completion when typing an editor's user name prefix.</p>

<p><strong>Steps to reproduce:</strong></p>

<ol>
<li>Find a post by AUser that was edited by UserB</li>
<li>Write a comment addressing <code>@UserB</code></li>
</ol>

<p><strong>Expected results:</strong></p>

<p>When having typed <code>@U</code>, the completion popup should suggest <code>@UserB</code></p>

<p><strong>Actual results:</strong></p>

<p>No popup, as if there were no such user in the list of addressable users.</p>

<blockquote>
  <p><img src="https://i.sstatic.net/i0wt0.png" alt="enter image description here"></p>
</blockquote>

<hr>

<p><a href="http://meta.stackexchange.com/questions/43019/how-do-comment-replies-work/43020#43020">The Meta post on this feature states</a>; while referencing <a href="http://meta.stackexchange.com/questions/36052/allow-post-editor-to-see-comments-directed-at-him/36055#36055">this answer</a>:</p>

<blockquote>
  <p>Notifications apply to the author, commenters, and editors of the question or answer that you are commenting on—users not in that list cannot be notified. You can also notify a ♦ moderator who closed the question. </p>
</blockquote>

<p>The popup can easily be seen as an indicator whether the user whose name I'm typing will receive my message, since, while typing a user's name and the name disappears from the suggestion list, it means I mistyped and the user will not be notified.</p>

<p>This behavior suggests that editors will not be notified at all, <a href="http://superuser.com/questions/252673/asus-eee-win7-x86-service-pack-1-failure-code-80073701-unknown-error">while they actually are</a>. This is why I classified this as a <strong>bug</strong>.</p>