UTF-8 characters are converted to their HTML entities which is not valid for XML

There's a statement in lib/php-excel.php which converts UTF-8 characters to their HTML entities (php function htmlentities), which produces invalid XML as only &gt;, &lt;, &amp; and &quot; are allowed. Apparently this characters are already converted anyway, if the line is removed valid XML is produced (even when <, >, & and " appear in the content, they appear correctly converted in the result).