To reproduce:

Public Class Form1
    Sub New()
         
        InitializeComponent()

        Me.RadScheduler1.EnableExactTimeRendering = True
        
        Dim dt = DateTime.Now
        Me.RadScheduler1.Appointments.Add(New Appointment(dt.AddMinutes(-10).AddSeconds(1), Now, "A1"))
        Me.RadScheduler1.Appointments.Add(New Appointment(dt.AddMinutes(-15), DateTime.Now.AddMinutes(-10), "A2"))
        Me.RadScheduler1.GetTimelineView().StartDate = DateAdd(DateInterval.Minute, -15, Now)

        Dim customScale As CustomTimescalePerMinute = New CustomTimescalePerMinute()
        Dim timelineView As SchedulerTimelineView = Me.RadScheduler1.GetTimelineView()
        timelineView.SchedulerTimescales.Add(customScale)

        timelineView.ShowTimescale(customScale)
        Dim currentScaling As SchedulerTimescale = timelineView.GetScaling()
        currentScaling.DisplayedCellsCount = 15
    End Sub
End Class

Public Class CustomTimescalePerMinute
Inherits MinutesTimescale
    Public Overrides ReadOnly Property ScalingFactor() As Integer
        Get
            Return 1
        End Get
    End Property
End Class

Note: the attached gif file illustrates the behavior. Initially, the first appointment's end is not rendered in the correct time slot. After scrolling, it is displayed correctly.

Workaround: force scrolling

Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    Dim t As SchedulerTimelineViewElement = TryCast(Me.RadScheduler1.SchedulerElement.ViewElement, SchedulerTimelineViewElement)
    Dim value = t.NavigationElement.Value
    t.NavigationElement.Value += 1
    Me.RadScheduler1.SchedulerElement.RefreshViewElement()
    t.NavigationElement.Value = value
End Sub

To reproduce:
Resource lResource;
var LColors = new Color[5];
SchedulerMultiDayView multyDayView;
DateTime startDate;

int interval;

radScheduler1.Statuses.Add(new AppointmentStatusInfo(5, "New", Color.Green, Color.Green, AppointmentStatusFillType.Solid));
radScheduler1.Statuses.Add(new AppointmentStatusInfo(6, "ACCP", Color.DarkOrange, Color.DarkOrange, AppointmentStatusFillType.Solid));


lResource = new Resource();
lResource.Id = new EventId(1);
lResource.Name = "Bert";
lResource.Color = Color.Red;

radScheduler1.Resources.Add(lResource);

radScheduler1.ActiveView.ShowHeader = true;

this.radScheduler1.ActiveViewType = SchedulerViewType.MultiDay;
multyDayView = this.radScheduler1.GetMultiDayView();

startDate = DateTime.Today;
interval = 30;

radScheduler1.GroupType = GroupType.Resource;
multyDayView.Intervals.Add(startDate, interval);

multyDayView.RulerScaleSize = 4;
radScheduler1.EnableExactTimeRendering = true;

multyDayView.RangeFactor = ScaleRange.Hour;

To reproduce:

Color[] colors = new Color[]
{
    Color.LightBlue, Color.LightGreen, Color.LightYellow,
    Color.Red, Color.Orange, Color.Pink, Color.Purple, Color.Peru, Color.PowderBlue
};
Random rand = new Random();
for (int i = 0; i < 25; i++)
{
    Resource resource = new Resource();
    resource.Id = new EventId(i);
    resource.Name = i + ".Resource";
    resource.Color = colors[rand.Next(0, colors.Length)];
    this.radScheduler1.Resources.Add(resource);
}

this.radScheduler1.GroupType = GroupType.Resource;
this.radScheduler1.ActiveView.ResourcesPerView = this.radScheduler1.Resources.Count;

for (int i = 0; i < 3; i++)
{
    Appointment a = new Appointment(DateTime.Now.AddHours(i), TimeSpan.FromMinutes(30), "A" + i);
    a.ResourceId = this.radScheduler1.Resources.Last().Id;
    this.radScheduler1.Appointments.Add(a);
}

NOTE: it is also valid for the horizontal scrollbar in Timeline view.

Workaround: use the SetResourceSize to increase the last resource's width a little bit: http://docs.telerik.com/devtools/winforms/scheduler/views/grouping-by-resources

To reproduce:

RadScheduler radScheduler1 = new RadScheduler();

public Form1()
{
    InitializeComponent();
    this.Controls.Add(this.radScheduler1);
    this.radScheduler1.Dock = DockStyle.Fill;

    Timer timer = new Timer();
    timer.Interval = 1000;
    timer.Tick += timer_Tick;
    this.radScheduler1.ActiveViewType = SchedulerViewType.Timeline;
    SetupView(DateTime.Now.Date);
    timer.Start();
}

private void SetupView(DateTime currentDateTime)
{
    SchedulerTimelineView timelineView = radScheduler1.GetTimelineView();
   
    timelineView.RangeStartDate = currentDateTime;
    timelineView.RangeEndDate = currentDateTime.AddHours(23).AddMinutes(59).AddSeconds(59);
    timelineView.StartDate = currentDateTime;
    radScheduler1.FocusedDate = currentDateTime;
    var scale = Timescales.Hours;
    timelineView.ShowTimescale(scale);
    var currentScaling = timelineView.GetScaling();
    currentScaling.DisplayedCellsCount = 24;

    this.radScheduler1.SchedulerElement.RefreshViewElement();
}

int count = 1;
private void timer_Tick(object sender, EventArgs e)
{
    SetupView(DateTime.Now.AddDays(++count));
}

Workaround: SchedulerTimelineView .ShowNavigationElement = false;

To reproduce:

public RadRibbonForm1() 
{
    InitializeComponent();

    this.radScheduler1.FocusedDate = new DateTime(2016, 1, 1);
    this.radScheduler1.ActiveViewType = Telerik.WinControls.UI.SchedulerViewType.Timeline;
    SchedulerTimelineView timelineView = this.radScheduler1.GetTimelineView();       
    timelineView.RangeStartDate = new DateTime(2016, 1, 1, 00, 00, 00);
    timelineView.RangeEndDate = new DateTime(2016, 12, 31, 23, 59, 59);
    timelineView.StartDate = new DateTime(2016, 1, 1, 00, 00, 00);

    Appointment appointment = new Appointment(new DateTime(2016, 1, 1, 00, 00, 00), new DateTime(2016, 1, 10, 00, 00, 00), "Quarter 1");
    Appointment appointment2 = new Appointment(new DateTime(2016, 2, 1, 00, 00, 00), new DateTime(2016, 2, 10, 00, 00, 00), "Quarter 1");
    Appointment appointment3 = new Appointment(new DateTime(2016, 4, 1, 00, 00, 00), new DateTime(2016, 4, 10, 00, 00, 00), "Quarter 2");
    Appointment appointment4 = new Appointment(new DateTime(2016, 5, 1, 00, 00, 00), new DateTime(2016, 6, 10, 00, 00, 00), "Quarter 2");
    Appointment appointment5 = new Appointment(new DateTime(2016, 7, 1, 00, 00, 00), new DateTime(2016, 7, 10, 00, 00, 00), "Quarter 3");
    Appointment appointment6 = new Appointment(new DateTime(2016, 8, 1, 00, 00, 00), new DateTime(2016, 8, 10, 00, 00, 00), "Quarter 3");
    Appointment appointment7 = new Appointment(new DateTime(2016, 11, 1, 00, 00, 00), new DateTime(2016, 11, 10, 00, 00, 00), "Quarter 4");
    Appointment appointment8 = new Appointment(new DateTime(2016, 12, 1, 00, 00, 00), new DateTime(2016, 12, 10, 00, 00, 00), "Quarter 4");

    this.radScheduler1.Appointments.Add(appointment);
    this.radScheduler1.Appointments.Add(appointment2);
    this.radScheduler1.Appointments.Add(appointment3);
    this.radScheduler1.Appointments.Add(appointment4);
    this.radScheduler1.Appointments.Add(appointment5);
    this.radScheduler1.Appointments.Add(appointment6);
    this.radScheduler1.Appointments.Add(appointment7);
    this.radScheduler1.Appointments.Add(appointment8);

    QuarterTimescale qTimeScale = new QuarterTimescale(); 
    qTimeScale.DisplayedCellsCount = 4;
    timelineView.SchedulerTimescales.Add(qTimeScale);
    this.radScheduler1.GetTimelineView().ShowTimescale(qTimeScale); 
}

class QuarterTimescale : MonthTimescale
{
    public override int ScalingFactor
    {
        get
        {
            return 3;
        }
    }

    public override string Name
    {
        get
        {
            return "Quarter";
        }
    }
}

Please refer to the attached gif file illustrating how to reproduce the problem with the Demo application. When you define a new appointment with 24 months interval, it is expected to have this event every 2 years, not each year.

To reproduce: you can use the following code snippet as well:

MonthlyRecurrenceRule monthlyRecurrenceRule = new MonthlyRecurrenceRule(DateTime.Now, WeekDays.Monday, 2, 24);
Appointment a = new Appointment(DateTime.Now, TimeSpan.FromHours(3), "Test");
a.RecurrenceRule = monthlyRecurrenceRule;
this.radScheduler1.Appointments.Add(a);


Workaround:

 public Form1()
 {
     InitializeComponent();
     
     this.radScheduler1.AppointmentAdded += radScheduler1_AppointmentAdded;
 }

 private void radScheduler1_AppointmentAdded(object sender, AppointmentAddedEventArgs e)
 {
     MonthlyRecurrenceRule montlyRule = e.Appointment.RecurrenceRule as MonthlyRecurrenceRule;
     if (montlyRule != null)
     {
         CustomMonthlyRecurrenceRule rrule = new CustomMonthlyRecurrenceRule();
         rrule.Start = montlyRule.Start;
         rrule.End = montlyRule.End;
         rrule.Interval = montlyRule.Interval;
         rrule.Offset = montlyRule.Offset;
         rrule.WeekDays = montlyRule.WeekDays;
         rrule.WeekNumber = montlyRule.WeekNumber;
         rrule.FirstDayOfWeek = montlyRule.FirstDayOfWeek;
         rrule.Count = montlyRule.Count; 

         e.Appointment.RecurrenceRule = rrule;
     }
 }

 public class CustomMonthlyRecurrenceRule : MonthlyRecurrenceRule
 {
     public override bool MatchAdvancedPattern(DateTime date, DateTimeFormatInfo dateTimeFormat)
     {
         int monthIndex = this.Start.Value.Month - date.Month;
         DateTime calculatedNextDate = this.Start.Value.AddMonths(this.Interval);
         monthIndex = calculatedNextDate.Month - date.Month;
         if (calculatedNextDate.Year > date.Year)
         {
             return false;
         }
         if ((monthIndex % this.Interval) != 0)
         {
             return false;
         }

         if (0 != this.WeekNumber && !this.MatchWeekOfMonth(date, dateTimeFormat))
         {
             return false;
         }

         if (0 != this.DayNumber && !this.MatchDayOfMonth(date, dateTimeFormat))
         {
             return false;
         }

         if (this.WeekDays != WeekDays.None && !this.MatchDayOfWeekMask(date, dateTimeFormat.Calendar))
         {
             return false;
         }

         if (this.Offset != 0 && !this.MatchOffset(date, dateTimeFormat))
         {
             return false;
         }

         return true;
     }
 }

Please refer to the attached gif file.

To reproduce:

this.radScheduler1.ActiveViewType = Telerik.WinControls.UI.SchedulerViewType.Month;
SchedulerMonthView monthView = this.radScheduler1.GetMonthView();

monthView.WeekCount = 5;
monthView.EnableCellOverflowButton = false;
monthView.EnableAppointmentsScrolling = true;
monthView.ShowVerticalNavigator = false;

for (int i = 0; i < 5; i++)
{
    this.radScheduler1.Appointments.Add(new Appointment(DateTime.Now, TimeSpan.FromDays(2), "Test" + i));
}
for (int i = 5; i < 10; i++)
{
    this.radScheduler1.Appointments.Add(new Appointment(DateTime.Now.AddDays(7), TimeSpan.FromDays(2), "Test" + i));
}
for (int i = 10; i < 15; i++)
{
    this.radScheduler1.Appointments.Add(new Appointment(DateTime.Now.AddDays(14), TimeSpan.FromDays(2), "Test" + i));
}
this.radScheduler1.Appointments.Add(new Appointment(DateTime.Now.AddMinutes(5),TimeSpan.FromDays(8),"Last"));
this.radScheduler1.Appointments.Add(new Appointment(DateTime.Now, TimeSpan.FromDays(14), "A"));
this.radScheduler1.Appointments.Add(new Appointment(DateTime.Now.AddDays(7), TimeSpan.FromDays(20), "B"));

Workaround: use the cell overflow button: SchedulerMonthView.EnableCellOverflowButton=true.

public Form1()
{
    InitializeComponent();
    DateTime d = DateTime.Now.Date; 
    radScheduler1.Appointments.Add(new Appointment(new DateTime(d.Year, d.Month, d.Day, 1, 30, 0), new DateTime(d.Year, d.Month, d.Day, 1, 30, 0), "Appointment_Free_0", "", ""));
    radScheduler1.Appointments.Add(new Appointment(new DateTime(d.Year, d.Month, d.Day, 8, 30, 0), new DateTime(d.Year, d.Month, d.Day, 9, 0, 0), "Appointment_Free_0", "", ""));
    radScheduler1.Appointments.Add(new Appointment(new DateTime(d.Year, d.Month, d.Day, 11, 00, 0), new DateTime(d.Year, d.Month, d.Day, 11, 30, 0), "Appointment_Free_0", "", ""));

    radScheduler1.Appointments.Add(new Appointment(new DateTime(d.Year, d.Month, d.Day, 11, 0, 0), new DateTime(d.Year, d.Month, d.Day, 11, 0, 0), "Appointment_Free_0", "", ""));
    radScheduler1.Appointments.Add(new Appointment(new DateTime(d.Year, d.Month, d.Day, 10, 30, 0), new DateTime(d.Year, d.Month, d.Day, 11, 0, 0), "Appointment_Free_0", "", ""));
    radScheduler1.Appointments.Add(new Appointment(new DateTime(d.Year, d.Month, d.Day, 11, 00, 0), new DateTime(d.Year, d.Month, d.Day, 11, 30, 0), "Appointment_Free_0", "", ""));
    radScheduler1.Appointments.Add(new Appointment(new DateTime(d.Year, d.Month, d.Day, 11, 30, 0), new DateTime(d.Year, d.Month, d.Day, 12, 0, 0), "Appointment_Free_0", "", ""));
    radScheduler1.Appointments.Add(new Appointment(new DateTime(d.Year, d.Month, d.Day, 14, 0, 0), new DateTime(d.Year, d.Month, d.Day, 14, 30, 0), "Appointment_Free_0", "", ""));
    radScheduler1.Appointments.Add(new Appointment(new DateTime(d.Year, d.Month, d.Day, 15, 00, 0), new DateTime(d.Year, d.Month, d.Day, 15, 30, 0), "Appointment_Free_0", "", ""));

    radScheduler1.Appointments.Add(new Appointment(new DateTime(d.Year, d.Month, d.Day, 17, 30, 0), new DateTime(d.Year, d.Month, d.Day, 17, 30, 0), "Appointment_Free_0", "", ""));

    radScheduler1.ActiveViewType = SchedulerViewType.Day;

    radScheduler1.EnableExactTimeRendering = true;
}


Workaround: use a custom DayViewAppointmentsTable

 this.radScheduler1.ElementProvider = new MyElementProvider(this.radScheduler1);

public class MyElementProvider : SchedulerElementProvider
{
    public MyElementProvider(RadScheduler scheduler) : base(scheduler)
    {
    }

    protected override T CreateElement<T>(SchedulerView view, object context)
    {
        if (typeof(T) == typeof(DayViewAppointmentsTable))
        {
            return new CustomDayViewAppointmentsTable(view.Scheduler, view, (DayViewAppointmentsArea)context)as T;
        }

        return base.CreateElement<T>(view, context);
    }
}

public class CustomDayViewAppointmentsTable : DayViewAppointmentsTable
{
    public CustomDayViewAppointmentsTable(RadScheduler scheduler, SchedulerView view, DayViewAppointmentsArea area) : base(scheduler, view, area)
    {
    }
    
    protected override IEnumerable<AppointmentElement> CreateAppointmentElements()
    {
        if (this.View != null)
        {
            IList<IEvent> appointmentsInView = new List<IEvent>(this.View.Appointments);
            List<AppointmentElement> elements = DivideAppointmentToElements(appointmentsInView);
            elements.Sort(0, elements.Count, new DateTimeComparer(this.Scheduler));

            foreach (AppointmentElement currentAppointment in elements)
            {
                currentAppointment.RelatedAppointments.Clear();
                currentAppointment.DesiredBounds = new RectangleF();
            }

            foreach (AppointmentElement appointment in elements)
            {
                List<AppointmentElement> intersectingAppointments = this.GetAllAppointmentsInDay(appointment.Start.Day, elements);
                intersectingAppointments.Remove(appointment);
                appointment.RelatedAppointments = intersectingAppointments;
            }

            return elements;
        }
        else
        {
            return new List<AppointmentElement>();
        }
    }

    private List<AppointmentElement> GetAllAppointmentsInDay(int day, List<AppointmentElement> elements)
    {
        List<AppointmentElement> result = new List<AppointmentElement>();
        foreach (AppointmentElement appointment in elements)
        {
            if (appointment.Start.Day == day)
            {
                result.Add(appointment);
            }
        }

        return result;
    }

    private List<AppointmentElement> DivideAppointmentToElements(IList<IEvent> appointmentsInView)
    {
        List<AppointmentElement> childAppointments = new List<AppointmentElement>();
        TimeSpan startTime = TimeSpan.FromMinutes(this.GetDayViewBase().RulerStartScale * 60 + this.GetDayViewBase().RulerStartScaleMinutes);
        TimeSpan endTime = TimeSpan.FromMinutes(this.GetDayViewBase().RulerEndScale * 60 + this.GetDayViewBase().RulerEndScaleMinutes);

        foreach (IEvent app in appointmentsInView)
        {
            SchedulerDayViewBase dayView = this.GetDayViewBase();
            bool allDay = (dayView != null) ? dayView.IsAllDayEvent(app) : false;

            DateTime appStart = this.View.DefaultTimeZone.OffsetTime(app.Start, this.Scheduler.SystemTimeZone);
            DateTime appEnd = this.View.DefaultTimeZone.OffsetTime(app.End, this.Scheduler.SystemTimeZone);

            if (!allDay)
            {
                // Handle > 1 day appointments
                if (appStart.Day != appEnd.Day && !(appEnd.Day - appStart.Day == 1 && appEnd.TimeOfDay == TimeSpan.Zero))
                {
                    AppointmentElement appointment1 = this.CreateAppointmentElement(this.Scheduler, this.View, app);
                    appointment1.Start = appStart;
                    appointment1.End = DateHelper.GetEndOfDay(appStart);

                    if (appointment1.Start.TimeOfDay >= endTime)
                    {
                        appointment1.Start = new DateTime(appStart.Year, appStart.Month, 
                            appStart.Day, 0, 0, 0).Add(endTime).AddMinutes(-(int)this.GetDayViewBase().RangeFactor);
                    }

                    AppointmentElement appointment2 = this.CreateAppointmentElement(this.Scheduler, this.View, app);
                    appointment2.Start = appEnd.Date;
                    appointment2.End = appEnd;

                    if (appointment1.Start >= this.View.StartDate)
                    {
                        childAppointments.Add(appointment1);
                    }

                    if (appointment2.Start >= this.View.StartDate)
                    {
                        childAppointments.Add(appointment2);
                    }
                }
                else
                {
                    AppointmentElement appointment1 = this.CreateAppointmentElement(this.Scheduler, this.View, app);
                    appointment1.Start = appStart;
                    appointment1.End = appEnd;

                    if (appointment1.Start.TimeOfDay < startTime)
                    {
                        appointment1.Start = new DateTime(appStart.Year, appStart.Month, appStart.Day, 0, 0, 0).Add(startTime);
                    }

                    if (appointment1.Start.TimeOfDay >= endTime)
                    {
                        appointment1.Start = new DateTime(appStart.Year, appStart.Month, appStart.Day, 0,
                            0, 0).Add(endTime).AddMinutes(-(int)this.GetDayViewBase().RangeFactor);
                    }

                    if (appointment1.End.TimeOfDay > endTime)
                    {
                        appointment1.End = new DateTime(appEnd.Year, appEnd.Month, appEnd.Day, 0, 0, 0).Add(endTime);
                    }

                    if (appointment1.End.TimeOfDay <= startTime)
                    {
                        appointment1.End = new DateTime(appEnd.Year, appEnd.Month, appEnd.Day, 0, 0,
                            0).Add(startTime).AddMinutes((int)this.GetDayViewBase().RangeFactor);
                    }

                    childAppointments.Add(appointment1);
                }
            }
            else if (!dayView.ShowAllDayArea)
            {
                DateTimeInterval viewInterval = new DateTimeInterval(this.View.StartDate, DateHelper.GetEndOfDay(this.View.EndDate));

                AppointmentElement appointment1 = this.CreateAppointmentElement(this.Scheduler, this.View, app);
                appointment1.Start = appStart;
                appointment1.End = DateHelper.GetEndOfDay(appStart);

                DateTimeInterval interval = new DateTimeInterval(appStart, appointment1.End);
                if (interval.IntersectsWith(viewInterval))
                {
                    if (appointment1.Start.TimeOfDay < startTime)
                    {
                        appointment1.Start = new DateTime(appStart.Year, appStart.Month, appStart.Day, 0, 0, 0).Add(startTime);
                    }

                    if (appointment1.Start.TimeOfDay >= endTime)
                    {
                        appointment1.Start = new DateTime(appStart.Year, appStart.Month, appStart.Day, 0, 0,
                            0).Add(endTime).AddMinutes(-(int)this.GetDayViewBase().RangeFactor);
                    }

                    if (appointment1.End.TimeOfDay > endTime)
                    {
                        appointment1.End = new DateTime(appEnd.Year, appEnd.Month, appEnd.Day, 0, 0, 0).Add(endTime);
                    }

                    if (appointment1.End.TimeOfDay <= startTime)
                    {
                        appointment1.End = new DateTime(appEnd.Year, appEnd.Month, appEnd.Day, 0, 0,
                            0).Add(startTime).AddMinutes((int)this.GetDayViewBase().RangeFactor);
                    }

                    childAppointments.Add(appointment1);
                }

                DateTime startDate = appStart.AddDays(1).Date;
                AppointmentElement appointment2 = null;

                while (startDate <= appEnd.Date.AddDays(-1))
                {
                    appointment2 = this.CreateAppointmentElement(this.Scheduler, this.View, app);
                    appointment2.Start = startDate;
                    appointment2.End = DateHelper.GetEndOfDay(startDate);
                    interval = new DateTimeInterval(appointment2.Start, appointment2.End);
                    if (interval.IntersectsWith(viewInterval))
                    {
                        childAppointments.Add(appointment2);
                    }
                    startDate = startDate.AddDays(1);
                }

                DateTime endDate = appEnd.Date;
                DateTime endAppointmentDate = appEnd;
                appointment2 = this.CreateAppointmentElement(this.Scheduler, this.View, app);
                appointment2.Start = endDate;
                appointment2.End = endAppointmentDate;

                interval = new DateTimeInterval(endDate, endAppointmentDate);
                if (interval.IntersectsWith(viewInterval) && interval.Start != appStart)
                {
                    childAppointments.Add(appointment2);
                }
            }
        }

        return childAppointments;
    }

    private AppointmentElement CreateAppointmentElement(RadScheduler scheduler, SchedulerView view, IEvent appointment)
    {
        AppointmentElement appointmentElement = null;
        if (scheduler.AppointmentElementFactory != null)
        {
            appointmentElement = scheduler.AppointmentElementFactory.CreateAppointmentElement(scheduler, view, appointment);
        }
        else
        {
            appointmentElement = scheduler.ElementProvider.GetElement<AppointmentElement>(view, appointment);
        }
        return appointmentElement;
    }
}

In Outlook, when the appontment height should be smaller than the height needed to accommodate 1 line of text, the appointment status size is being changed instead.

To reproduce: follow the steps from the attached gif file.

Workaround:

public Form1()
{
    InitializeComponent();
    this.radScheduler1.RecurrenceEditDialogShowing += radScheduler1_RecurrenceEditDialogShowing;
}

CustomEditRecurrenceDialog dialog = null;

private void radScheduler1_RecurrenceEditDialogShowing(object sender, Telerik.WinControls.UI.RecurrenceEditDialogShowingEventArgs e)
{
    if (dialog == null)
    {
        dialog = new CustomEditRecurrenceDialog(e.Appointment);
    }
    e.RecurrenceEditDialog = dialog;
}

public class CustomEditRecurrenceDialog : EditRecurrenceDialog
{
    public CustomEditRecurrenceDialog(IEvent appointment) : base(appointment)
    {
    }

    protected override void ApplyAppointmentDates()
    {
        DateTime end = this.appointment.End;
        base.ApplyAppointmentDates();
        this.appointment.End = new DateTime(end.Year, end.Month, end.Day,
            this.timeEnd.Value.Hour, this.timeEnd.Value.Minute, this.timeEnd.Value.Second);
    }
}

Workaround: use your own icon: 

public Form1()
{
    InitializeComponent();
    this.radScheduler1.RecurrenceEditDialogShowing+=radScheduler1_RecurrenceEditDialogShowing;
}

private void radScheduler1_RecurrenceEditDialogShowing(object sender, Telerik.WinControls.UI.RecurrenceEditDialogShowingEventArgs e)
{
    ((RadForm)e.RecurrenceEditDialog).Icon = Properties.Resources.WinFormsIcon;
}

Please refer to the attached screenshots. A sample project is attached.

There is a known issue in the .NET Framework considering the "fa-IR" culture. Please refer to the following MSDN resource for a solution which is included in the sample project: https://code.msdn.microsoft.com/Fixing-Persian-Locale-for-6e66e044#content

Workaround:

 private void radScheduler1_CellFormatting(object sender, SchedulerCellEventArgs e)
        {
            MonthCellElement monthCellElement = e.CellElement as MonthCellElement;
            if (monthCellElement != null)
            {
                monthCellElement.Header.Text = monthCellElement.Date.ToString("dd", this.radScheduler1.Culture);
            }
        }

To reproduce: please refer to the attached gif file

Dim a1 As New Appointment(DateTime.Today.AddDays(-1), TimeSpan.FromDays(3), "Termin1")
a1.AllDay = True
Dim a2 As New Appointment(DateTime.Today.AddDays(-1), TimeSpan.FromDays(1), "Termin2")
a2.AllDay = True
Me.RadScheduler1.Appointments.Add(a1)
Me.RadScheduler1.Appointments.Add(a2)

Workaround: specify precisely the end date including the time part as well

Dim a1 As New Appointment(DateTime.Today.AddDays(-1), TimeSpan.FromDays(3).Add(TimeSpan.FromMinutes(1)), "Termin1")
a1.AllDay = False
Dim a2 As New Appointment(DateTime.Today.AddDays(-1), TimeSpan.FromDays(2).Add(TimeSpan.FromMinutes(1)), "Termin2")
a2.AllDay = False
 
Me.RadScheduler1.Appointments.Add(a1)
Me.RadScheduler1.Appointments.Add(a2)

To reproduce:

public Form1()
{
    InitializeComponent();

    this.radScheduler1.ActiveViewType = Telerik.WinControls.UI.SchedulerViewType.Timeline;
    this.radScheduler1.EnableGesture(Telerik.WinControls.GestureType.Pan);
    this.radScheduler1.DisableGesture(Telerik.WinControls.GestureType.Zoom);
    this.radScheduler1.ZoomGesture+=radScheduler1_ZoomGesture;
    this.radScheduler1.PanGesture+=radScheduler1_PanGesture;
}

private void radScheduler1_PanGesture(object sender, Telerik.WinControls.PanGestureEventArgs e)
{
    Console.WriteLine("Pan should fire");
}

private void radScheduler1_ZoomGesture(object sender, Telerik.WinControls.ZoomGestureEventArgs e)
{
    Console.WriteLine("Zoom should NOT fire");
}

Workaround:
public class CustomScheduler : RadScheduler
{
    public override string ThemeClassName
    {
        get
        {
            return typeof(RadScheduler).FullName;
        }
    }

    protected override void OnZoomGesture(Telerik.WinControls.ZoomGestureEventArgs args)
    {
        //stop the basic logic
        //base.OnZoomGesture(args);
    }
}

Please refer to the attached file.

Workaround: clear remind objects when the appointment is changed:
private void radScheduler1_AppointmentChanged(object sender, AppointmentChangedEventArgs e)
{
    schedulerReminder.ClearRemindObjects();        
    foreach (Appointment a in this.radScheduler1.Appointments)
            {
                schedulerReminder.AddRemindObject(a);
            }  
}

Workaround:
public class MyTimelineGroupingByResourcesElement : TimelineGroupingByResourcesElement
{
    public MyTimelineGroupingByResourcesElement(RadScheduler scheduler, SchedulerView view)
        : base(scheduler, view)
    { }

    public override void NavigateForward()
    {
        TimeSpan ts = (this.View as SchedulerTimelineView).RangeEndDate - this.View.StartDate;
        int differenceInDays = ts.Days;
        int displayedCells = (this.View as SchedulerTimelineView).GetScaling().DisplayedCellsCount;

        if (differenceInDays >= displayedCells)
        {
            base.NavigateForward();
        }
    }
}

public class MyElementProvider : SchedulerElementProvider
{
    public MyElementProvider(RadScheduler scheduler)
        : base(scheduler)
    { }

    protected override T CreateElement<T>(SchedulerView view, object context)
    {
        if (typeof(T) == typeof(TimelineGroupingByResourcesElement))
        {
            return new MyTimelineGroupingByResourcesElement(this.Scheduler, view) as T;
        }

        return base.CreateElement<T>(view, context);
    }
}

 public RadForm2()
        {
            InitializeComponent();

            this.radScheduler1.ElementProvider = new MyElementProvider(this.radScheduler2);
        }

To reproduce: use the following code snippet:

private BindingList<MyEvent> eventsSource = new BindingList<MyEvent>();
private AppointmentMappingInfo appointmentMappingInfo_g = new AppointmentMappingInfo();

public RadForm2()
{
    InitializeComponent();
}

private void RadForm2_Load(object sender, EventArgs e)
{
    radScheduler1.ActiveViewType = radScheduler2.ActiveViewType = SchedulerViewType.Timeline;
    radScheduler1.GetTimelineView().ShowTimescale(Timescales.Days);
    radScheduler2.GetTimelineView().ShowTimescale(Timescales.Days);
    radScheduler1.GetTimelineView().RangeStartDate = radScheduler2.GetTimelineView().RangeStartDate = new DateTime(2015, 9, 1);
    radScheduler1.GetTimelineView().RangeEndDate = radScheduler2.GetTimelineView().RangeEndDate = new DateTime(2015, 9, 30);
    radScheduler1.GetTimelineView().StartDate = radScheduler2.GetTimelineView().StartDate = new DateTime(2015, 9, 1);
    radScheduler1.GetTimelineView().GetScaling().DisplayedCellsCount = radScheduler2.GetTimelineView().GetScaling().DisplayedCellsCount = 7;

    appointmentMappingInfo_g.Start = "Start";
    appointmentMappingInfo_g.End = "End";
    appointmentMappingInfo_g.Summary = "Subject";
    appointmentMappingInfo_g.Description = "Description";
    appointmentMappingInfo_g.Location = "Location";
    appointmentMappingInfo_g.UniqueId = "Id";

    SchedulerBindingDataSource dataSource_l = new SchedulerBindingDataSource();
    dataSource_l.EventProvider.Mapping = appointmentMappingInfo_g;
    dataSource_l.EventProvider.DataSource = eventsSource;
    radScheduler2.DataSource = dataSource_l;

    FillAppointments();
}

private void FillAppointments()
{
    Appointment appointment = new Appointment(new DateTime(2015, 9, 2), new DateTime(2015, 9, 6), "DU 2 AU 6");
    appointment.AllDay = true;

    radScheduler1.Appointments.BeginUpdate();
    radScheduler1.Appointments.Add(appointment);
    radScheduler1.Appointments.EndUpdate();

    MyEvent appointment2 = new MyEvent(new DateTime(2015, 9, 2), new DateTime(2015, 9, 6), "DU 2 AU 6","","","");
    radScheduler2.Appointments.BeginUpdate();
    eventsSource.Add(appointment2);
    radScheduler2.Appointments.EndUpdate();
}

public class MyEvent
{
    public DateTime Start { get; set; }

    public DateTime End { get; set; }

    public string Subject { get; set; }

    public string Description { get; set; }

    public string Location { get; set; }

    public string UniqueId { get; set; }

    public MyEvent(DateTime start, DateTime end, string subject,
        string description, string location, string uniqueId)
    {
        this.Start = start;
        this.End = end;
        this.Subject = subject;
        this.Description = description;
        this.Location = location;
        this.UniqueId = uniqueId;
    }
}

Workaround: specify the end day with 1 second more:
 MyEvent appointment2 = new MyEvent(new DateTime(2015, 9, 2), new DateTime(2015, 9, 6, 0, 0, 1), "DU 2 AU 6", "", "", "");