While reviewing MDL-42301 I noticed the following error when I deleted a course from the course management interface

Stack trace:

    line 393 of /lib/setuplib.php: coding_exception thrown

    line 2639 of /lib/coursecatlib.php: call to default_error_handler()

    line 1434 of /lib/coursecatlib.php: call to course_in_list->__construct()

    line 451 of /course/classes/management_renderer.php: call to coursecat->get_courses()

    line 421 of /course/management.php: call to core_course_management_renderer->course_listing()

The reason for the error was get_courses was returning an outdated list of courses. However during the course delete process fix_course_sortorder() is called , which is supposed to purge the related caches, but that is not what is happening. For some reason the caches are not purged and hence the error is generated.
I tried using cache_helper::purge_by_event('changesincoursecat'); and the error still persists, however if I purge the catch by definition for 'coursecat' in delete_course() , everything works as expected.

This is an edge case scenario , I am able to reproduce this only in one of my Moodle installs. All other installs work as expected. I do not have any noticeable difference in settings between the installs, hence am not exactly sure how to replicate it on a fresh install.