To reproduce: please refer to the attached sample project and run it. Try to edit the existing appointment by using the inline editor. As a result, the AppointmentAdded event will be fired. You will notice that the Appointments collection contains more appointments than the existing ones. Note that if you use the edit dialog, this event is not fired and the behavior is as expected.

Workaround: RadScheduler1.SchedulerElement.EditorManager.EditorViewMode = SchedulerEditorViewMode.EditorDialog