Feedback Comments wiped if one grade missing in Grading Guide

If a teacher accidentally misses entering one numerical grade for one criteria in an Assignment with a Grading Guide, the text in the "Feedback comments" section is wiped upon clicking "Save changes" or "Save and show next."

Video demonstration here:

https://www.loom.com/share/7014f565f4f84c4ab2ddac668d36971d

Steps to reproduce:

1. Create a course
2. Add an assignment with a grading guide
3. Grade a student in that assignment
4. Enter grades for all but one criteria in the grading guide
5. Enter text in the Feedback Comments section at the end
6. Click Save changes
7. Feedback comments are deleted (we use the default Atto editor, FYI)

We are on 3.8.4 but I don't see that as an option under "Affects Version."