I'm currently working on a course format (which is intended to be submitted to the Moodle plugins directory once complete).

This course format makes use of the Moodle comments API.

This works perfectly, until you try and restore from backup, at which point you get a fatal error:
Exception - Call to undefined method restore_course_task::get_comment_mapping_itemname()

This function is defined in restore_activity_task, so it is not available in restore_course_task.

It looks like moving the function up one level into restore_task solves the problem