Configuration warning intermittently shown, despite configuration being defined

Before a user is logged in to WordPress, the plugin does not add config=default to the URL, resulting in the following error message:

MathJax no longer loads a default configuration file; you must specify such files explicitly. This page seems to use the older default config/MathJax.js file, and so needs to be updated. This is explained further at
https://www.mathjax.org/help/configuration

After the user has logged in, the config parameter appears and the plugin works as expected.

When the plugin does not add the parameter, the following script appears in the footer:

<script type='text/javascript' src='https://c328740.ssl.cf1.rackcdn.com/mathjax/latest/MathJax.js'></script>
And when it does (and there is no warning message), this is in the footer:

<script type='text/javascript' src='https://c328740.ssl.cf1.rackcdn.com/mathjax/latest/MathJax.js?config=default'></script>

(The hardcoded Rackspace script is used as accessing the default MathJax CDN URL over https (https://cdn.mathjax.org/mathjax/latest/MathJax.js?config=default) gives a certificate warning. However, I have verified that this issue is independent of this – it exists when I use the normal CDN link with http too.)

I have tried setting the URL “config” parameter to different values (e.g. “Accessible” and “TeX-AMS-MML_HTMLorMML”) but I get the same intermittent issue.

Executing MathJax.Message.Log() when the incorrect CDN link is loaded gives the following:

Loading [MathJax]/extensions/v1.0-warning.js
Loading [MathJax]/extensions/MathMenu.js
Loading [MathJax]/extensions/MathZoom.js

See here for a screenshot of my WordPress MathJax plugin page.