Thanks Teresa for your reply.
Perhaps an actual example will help. The students in this class are allowed to self-select their groups and given one weeks time to decide. The first group of students formed their group on day 1. I created a group, team 1, and added these students to this group. Then after a couple of days, the second team was formed. When I created the second group (team 2), the name of a student from the Team 1 was deleted even though I did not delete this student. When the third team was formed, the names of three students from Team 1 was deleted. In fact, these three students names did not appear even on the participants list. Why does this happen? It is a "standard discussion forum" with visible groups.
Sadhus