Bug#859572: docbook-xsl: randomly adds ???TITLE??? to title

[Chris West <solo-debianbugs@goeswhere.com>]

Package: docbook-xsl
Version: 1.79.1+dfsg-2

Sometimes, when I generate HTML, the title for my book gets
"???TITLE???" appended to it. This happens for very simple books:

$ cat usersBook.xml
<?xml version="1.0"?>
<book xmlns="http://docbook.org/ns/docbook";>
<title>foo</title>
<appendix>
<para>
</para>
</appendix>
</book>

$ xsltproc --output html/ \
  --xinclude \
  /usr/share/xml/docbook/stylesheet/docbook-xsl/htmlhelp/htmlhelp.xsl \
  usersBook.xml
...
Request for title of element with no title: code (contained in )
...
$ grep '^Title=' html/htmlhelp.hhp
Title=foo???TITLE???

However, sometimes it does not. The "Request.." message is omitted, and
the title is normal:
Title=foo

This happens ~60% of the time.

This affects the reproducibility of packages such as gsequencer, due to
the random variation it introduces.

My investigation:
Sometimes, a <code> element is generated during glossary generation.
(I don't know why this happens.). Then, this template matches:
<xsl:template match="*" .. in .../docbook-xsl/common/titles.xsl
..which returns ???TITLE??? as the <code> doesn't exist anywhere with a
title... and it gets stuck in the raw title, then.. I got super lost.