Steps to replicate

1. Create a course.
2. Create a quiz.
3. Add an essay-type question.
4. Keep the required field of the form remains empty. Click the Save Changes button at the bottom of the form.
5. You will see required warnings on the Question name  and Question text.
6. Enter something in the question name and leave the question text empty.
7. Click the Save Changes button at the bottom of the form.
8. You will see the required warnings on the Question text.
9. Enter something and then click the "tab" keyboard to leave the editor.

EXPECTED

The required warning on the Question text is gone.

ACTUAL

The required warning on the Question text remains visible.