Steps:

1. Create new user in Editors user group
2. Co to Admin/Content Types/Users/User and click edit
3. Mark as checked any password policy, for example: Password must contain at least one number and update
4. Go to edit mode of user created in step 1.
5. Edit the password and repeat password, don't use numbers
6. Click Update

Actual result:

Password validation is displayed. Username is empty. If I provide correct password, I can't update, because of empty username field.

Expected result:

Username should not be empty.