Acknowledgement title in articles?

The Markup UK proceedings currently has two <article> that include an
<acknowledgements>, one with a <title> and one without.  See pages 12
and 124 of:

   https://markupuk.org/2019/Markup-UK-2019-proceedings.pdf

The 1.79.1 stylesheets (and, seemingly, the current GitHub stylesheets
[1]) neither generate a title nor show the provided title.  What is the
reasoning behind this?

Regards,


Tony Graham.
--
Senior Architect
XML Division
Antenna House, Inc.
----
Skerries, Ireland