Could the property be allowed to add defect to the role template? There may be cases where the person assigned as Author should not open the defect. As an example, the Author can only fix the defect ...
Since the main purpose of peer review is to find defects, it seems unecessary (and counterproductive) to prevent any role, including the Author, from reporting them. For conflict of interest reasons, I could see that possibly you would want to avoid a process that only allowed the Author to enter defects, but if other participants can enter them (as they should), why not allow the Author to enter them too? Blocking any review role from entering defects introduces the risk of them being missed.