The recent activity block has a function to show recent enrolments. This currently doesn't work, probably because of the way recent enrolments are checked (it's done in a function, declared in deprecated lib) - it's based on enrolment logs, which are not recorded for some reason. It might be better to check user's role assignment record in course for timemodified field. In this way, recent enrolments are shown correctly. This is implemented in attached patch (apply with -p0).