Below I have listed the method to reproduce the problem.
Open the Telerik WPF Controls Examples > ScheduleView > Features > Configurator.
Check "Snap Appointments" and set "Day Start Time" to for example 08:00.
Start dragging an appointment to start time 08:00, nothing strange will happen, when you now drag the appointment a little bit higher (so the start time will be earlier) the appointment disappears.
I assume this is a bug?
Can you help on this? (maybe a workaround?)