Steps to reproduce:

• create a course with an instructor, log in as the instructor, edit course
• create a Forum activity
• give the Forum a name & under Whole forum grading turn on grading by making a selection (e.g. type = "scale" with method = "simple direct grading")
• save and display the Forum, then select Grade users
• you are asked to grade…yourself, the instructor

Desirable behavior:

• wherever grading occurs, it should obey the Gradebook's "gradebookroles" setting and omit roles which are not included there

The problem is broader than this minimal recreation outlines: users in any non-student role are included in grading (Manager, TA, etc.). It does not appear to matter what grading settings you employ on the Forum, I tried a variety of combinations but the Instructor always appeared in the grading interface.