Wikimedia Bugzilla is closed!

While Flow changed anonymous IP handling, blank IP addresses led to topic participants appearing in a white typewriter text block.  This happened because wikitext parsing of a message starting with a blank results in pre-formatted text.  In eval.php,
  echo wfMessage( 'flow-topic-participants', 2, 2, '', 'second person' )->parse();
(note the empty string for first participant); this prints

<pre>and second person
</pre>

We fixed that bug, but it's wasted effort doing this level of wikitext parsing if we don't need to, and it's prone to embarrassing HTML output. Niklas on mediawiki-i18n list commented
  Is there any other wikitext besides the magic words? You could just use ->text() instead of ->parse().

and sure enough if you call text() instead you avoid the additional parsing.  I didn't test this message's complex GENDER handling in a language where it matters, but we should check all our messages using parse() (about 13 of them in PHP) and see if we can switch them to ->text(), or escaped() if they're directly output, or even plain(). See https://www.mediawiki.org/wiki/Manual:Messages_API . Use of parse() where we don't intend to be converting wikitext constructs into HTML seems about 25% slower on this string in my dopey testing, and could cause some display bugs.