After a bit of dithering on this, I'm pretty sure that Mark's revision of
the plugin is working under the current version of WordPress I'm testing on
(3.4.2). I have a few other things I'm going to need to do before I declare
this solved, upgrade the Journal's instance of WordPress and upload the
updated plugin to GitHub, but I wanted to say thanks in advance. The
Code4Lib community is incredible!

Tom