This is resolved in the next version of the installer. When making a fresh install of 4.0.11 or higher, the admin will be prompted to either
- enter a name for a new moderator group
- select an existing usergroup that qualifies (NOT guests, administrators, banned groups, or groups that don't allow permissions from other groups)
In this way, in most scenarios, the forum should never wind up with unwanted moderator groups, so long as the admin responds to this prompt appropriately. Uninstall will still not remove the selected usergroup, since, as I mentioned earlier, there is no way to know if that group is still being used in some way for non-wiki permissions.