If a teacher is going through the list of enrolled users and unenrolling lots of users, they can easily unenrol themselves too. This throws them out of the course and they obtain an error message "Sorry, but you do not currently have permissions to do that (Review course enrolments)".

In 1.9 it was possible to prevent teachers from accidentally unenrolling themselves http://docs.moodle.org/19/en/Enrolment_FAQ#How_do_I_prevent_teachers_from_unenrolling_themselves_from_their_course_by_mistake.3F but in Moodle 2 preventing the capability enrol/manual:unenrolself for the teacher role has no effect.