When importing content from one course to another (via the "Course import" facility), all groups from the source course are always copied (i.e., created as empty groups) in the target course. This applies even if only one individual activity is being imported, without user data.

This behaviour is not always desired. in fact, it is particularly annoying when teachers import content from several courses they've given in the past. They end up with a long list of empty groups in their course, sometimes identically named to (but distinct from) the groups they actually use in the present course.

To reproduce: Create two courses, C1 and C2. Create one activity in C1 (the News Forum suffices), and create one group in C1. Go to C2, click "Course administration -> Import", and choose C1 as the source course. Select only "Include activities" and select only one activity to be imported. C2 will now contain the group from C1.