In 2.9.x, after entering an invalid grade for the grade override, the input box is reset to the old value, which can be confusing to users. In 2.8.x, the invalid value that was entered is kept in the input box for the user to see the error of their ways.
See the attached screenshots. I entered an invalid grade of "k". In 2.8.x, the value of "k" stays in the field, whereas in 2.9.x, the field reverts to the previous value of "A", but the error messages says that I need to enter a valid grade. This is confusing, especially if I am entering a large number of overrides.