This is by design. Global change windows and blackout windows will always be shown on the Change Calendar.
It is not possible to show non-Global change windows on the Change Calendar. The change calendar is primarily used to identify change conflicts. Therefore, it makes sense to show blackout windows and global maintenance windows additionally to scheduled change orders.
Individual maintenance windows for a specific CIs will not generally harm other change orders as long as these CIs do not belong to scheduled change orders.