Moodle Version: Moodle 3.5.2+ (Build: 20180920)
This was working fine after an upgrade to v3.5, but seemed to break after a subsequent upgrade to v3.5.1. I've upgraded to the latest and greatest, with no improvement. Can anyone else verify that this is occurring for them? It's when you go into the Gradebook setup section of a course.
I've checked with several themes, and this appears to be a Moodle issue, not a theme issue.