Fail XHTML Strict Validation

I got a xhtml strict 1. 0 validation failure with the guestbook module.

document type does not allow element "div" here; missing one of "object", "ins", "del", "map", "button" start-tag.

…file.">kilroy</a><div class="picture"><a href="/1_Development/Project/

Appears this is coming from the user picture being inside a <b> element:

<b>
  <a title="View user profile." href="/1_Development/ProjectL/users/kilroy">kilroy</a>
  <div class="picture">
  <a title="View user profile." href="/1_Development/Project/users/kilroy">
    <img title="kilroy's picture" alt="kilroy's picture" src="http://localhost:8888/1_Development/Project/files/avatar_selection/icons09.jpg"/>
  </a>
  </div>
</b>

In guestbook.module about line 665 if remove the <b> elements then it'll validate fine

// Author.
  if ($entry['author'] == 0) {
    $author = check_plain($entry['anonname']);
    //$author = "<b>". check_plain($entry['anonname']) ."</b>";
  }
  else {
    $author = theme('guestbook_user_picture', $entry['author']);
    //$author = "<b>". theme('guestbook_user_picture', $entry['author']) ."</b>";
  }

  $output .= '<div class="author">'. $author .'</div>';