Well, there’s nothing like quickly pushing an update after your initial release! After all the initial testing that went into the version of DisableMU which I submitted to the repository, it turned out there was a severe failure in the logic used when determining where to inject the Constants which I needed to override with the plugin.
Due to the fact that wp-settings.php is included just before the end of the file, that was in turn including default-constants.php which defines the values of the /mu-plugin directory & url. That meant that by the time WordPress got to my definitions… it ignored them.
This meant no harm was done by the installation of the plugin, but it also meant that nothing was effectively happening by using the plugin! Initial tests to confirm the value of the Constants were done prior to the final coding which injected at the end of the file, which just goes to prove that you should always check your work! No matter how confident you are in it, each change you make in the development process has the potential to have unexpected consequences.