I've tested across a couple of sites, versions of moodle, and different themes to try and rule out this being something on our side, but it appears fairly consistent.

Create a course, and set up "manual completion by others" - set that to be completable by a teacher
Enrol yourself as a teacher on said course, and enrol any test student
Head to the course completion report and tick the manual completion button.

You should see yourself redirected the the home page, whether that is set to your dashboard or the site front page. This seems erroneous.