In the course of trying to solve the problem in this discussion: https://moodle.org/mod/forum/discuss.php?d=271441 I found out that the Lesson progress bar never displays a 100% progress on the very last page of a lesson!
This can be very easily fixed by adding a link to the relevant function. In current moodle 2.7 version, file mod/lesson/view.php, after line 431
if (!$canmanage) {
add this line:
$lessoncontent .= $lessonoutput->progress_bar($lesson);
Joseph
See result:
You may wish to vote for issue MDL-47587 in the tracker so that someone at Moodle HQ may fix it some time.