Steps to reproduce:

1. As admin, create a new course.
2. Add a grade item with certain settings.
3. Log in as 'Bad teacher', and change some of the grade items settings.
4. Log in as admin, and visit the gradebook.

Actual results:

• The settings are now wrong, but you don't know who changed them.

Expected result:

• You should be able to go to Course administration -> Logs, to see who made the change, so you can discus it with them.

Partial work-around:

• The grade history report gives you some information.

All singificant changes made in Moodle should be logged, therefore, I think, the missing events here should be considered a bug.