The problem here was that user/index.php checks the system level
capability moodle/site:viewparticipants when the user is on the front
page, and the moodle/course:viewparticipants on non-front pages.
But the navigation displayed the link by mistake even in situations,
when the user has the capability moodle/course:viewparticipants on the
front page (typically when the default role for the front page is set to
student).
Added behat tests for reproducing the bug and also for checking the
basic functionality of the feature.
57b81c93f5