When creating a backup in Moodle 2.8 I get

error/element_already_used_for_annotation

$a contents: stdClass Object

(

[attribute] => teacher

[annotating] => user

)

Stack trace:
line 46 of /backup/util/structure/backup_final_element.class.php: base_element_struct_exception thrown
line 248 of /backup/util/structure/backup_nested_element.class.php: call to backup_final_element->set_annotation_item()
line 77 of /mod/qcreate/backup/moodle2/backup_qcreate_stepslib.php: call to backup_nested_element->annotate_ids()
line 88 of /backup/util/plan/backup_structure_step.class.php: call to backup_qcreate_activity_structure_step->define_structure()
line 181 of /backup/util/plan/base_task.class.php: call to backup_structure_step->execute()
line 214 of /backup/moodle2/backup_activity_task.class.php: call to base_task->execute()
line 177 of /backup/util/plan/base_plan.class.php: call to backup_activity_task->execute()
line 120 of /backup/util/plan/backup_plan.class.php: call to base_plan->execute()
line 320 of /backup/controller/backup_controller.class.php: call to backup_plan->execute()
line 111 of /backup/util/ui/backup_ui.class.php: call to backup_controller->execute_plan()
line 131 of /backup/backup.php: call to backup_ui->execute()