To reproduce:

Appointment a1 = new Appointment(DateTime.Today.AddHours(10).AddMinutes(30), TimeSpan.FromMinutes(30), "A1");
Appointment a2 = new Appointment(DateTime.Today.AddHours(11) , TimeSpan.FromMinutes(30), "A2");
Appointment a3 = new Appointment(DateTime.Today.AddHours(11).AddMinutes(30), TimeSpan.FromMinutes(30), "A3");
this.radScheduler1.Appointments.Add(a1);
this.radScheduler1.Appointments.Add(a2);
this.radScheduler1.Appointments.Add(a3); 
this.radScheduler1.ActiveViewType = SchedulerViewType.Timeline;   
SchedulerTimelineView timelineView = radScheduler1.GetTimelineView();
timelineView.ShowTimescale(Timescales.Minutes);
timelineView.GetScaling().DisplayedCellsCount = 10;

Please refer to the attached sample project which incorrect behavior when scrolling is illustrated in the attached gif file.

Workaround: instead of specifying 30 minutes duration of an appointment, use 29 minutes and 59 seconds.