There are two errors when restoring a course that relates to groups:
1. When restoring a course backup the students enrolled in the course don't get assigned to their groups.
2. A empty field IS restored to the groups (Existing members: 1, when empty and 2 when one student is added) and the groups is indicated that they have one member. This "invisble" member can be removed from the course. When removed it doesn't get moved over to the list of students.