Unable to edit permissions of 'Artist->Field Permissions->Task->Reviewer'

Hi there! We’ve been setting up a process for our Studio on ShotGrid. Recently we’ve discovered that an Artist on their Task Page could EDIT the Reviewer (Renamed as Supervisor). I tried to check permission and wanted to remove it from being Edited, but the Configure field is Disabled for all roles, including Admin, Manager, Supervisor, and Artists.

I also tried via the People-Permissions page, and I’m unable to edit permissions of ‘Field Permissions->Task->Reviewer’

Is this a bug, or is there a way to restrict the Artist from Editing the Reviewer, aka Supervisor?