When trying to delete Course Set 1 (having already made at least one other new course set, to enable the option), the course set will simply reappear (empty, with no classes in it) after a page refresh.

Also, prior to that page refresh, the courses that were in Course Set 1 will get put into all other course sets, temporarily. They will only show in the calendar (not in the list of courses beneath it). If the addition of one of these courses creates a conflict, the usual "uh oh! conflict..." message will display. Once the page has been refreshed, the course sets go back to normal (aside from Course Set 1, which is back from the dead, and empty).

I haven't been able to find any similar behavior with any course set except for Course Set 1.