In Moodle 2.7.1 whenever you duplicate an activity the following entries are generated in the apache log:

[:error] [pid 2083] [client ip:52336] Looking at a task, referer: https://domain/elearning/moodle/course/view.php?id=5&notifyeditingon=1
[:error] [pid 2083] [client ip:52336] Looking at a task, referer: /elearning/moodle/course/view.php?id=5&notifyeditingon=1
[:error] [pid 2083] [client ip:52336] Looking at a restore_activity_task task, referer: https://domain/elearning/moodle/course/view.php?id=5&notifyeditingon=1
[:error] [pid 2083] [client ip:52336] Contexts match, referer: https://domain/elearning/moodle/course/view.php?id=5&notifyeditingon=1

These messages come from course/lib.php

3476 // restored copy of the module
3477 $newcmid = null;
3478 $tasks = $rc->get_plan()->get_tasks();
3479 foreach ($tasks as $task) {
3480 error_log("Looking at a task");
3481 if (is_subclass_of($task, 'restore_activity_task')) {
3482 error_log("Looking at a restore_activity_task task");
3483 if ($task->get_old_contextid() == $cmcontext->id)

(Running ubuntu server 14.04 LTS)