public class CustomSchedulerInputBheavior : SchedulerInputBehavior
        {
            public CustomSchedulerInputBheavior(RadScheduler scheduler) : base(scheduler)
            {
            }

            Point mouseDownPosition = Point.Empty;
            public override bool HandleMouseDown(MouseEventArgs args)
            {
                mouseDownPosition = args.Location;
                return base.HandleMouseDown(args);
            }
            public override bool HandleMouseMove(MouseEventArgs args)
            {
                SchedulerCellElement cell = this.Scheduler.ElementTree.GetElementAtPoint(args.Location) as SchedulerCellElement;

                AppointmentElement appointment = this.Scheduler.ElementTree.GetElementAtPoint(args.Location) as AppointmentElement;
                if (appointment == null)
                {
                    appointment = this.Scheduler.ElementTree.GetElementAtPoint(this.mouseDownPosition) as AppointmentElement;
                }

                if (this.Scheduler.Behavior.ItemCapture != null && (this.Scheduler.Behavior.ItemCapture.Parent is RadScrollBarElement ||
                    this.Scheduler.Behavior.ItemCapture is RadScrollBarElement))
                {
                    return false;
                }

                if (this.Scheduler.Capture && args.Button == MouseButtons.Left)
                {
                     appointment = this.Scheduler.ElementTree.GetElementAtPoint(this.mouseDownPosition) as AppointmentElement;

                    FieldInfo fi = typeof(SchedulerInputBehavior).GetField("selecting", BindingFlags.Instance| BindingFlags.NonPublic);
                    bool selecting = (bool)fi.GetValue(this);
                    if (selecting)
                    {
                        if (cell != null && cell.AllowSelection && args.Button == MouseButtons.Left)
                        {
                            this.SelectCell(cell, true);
                        }
                    }
                    else if (this.Scheduler.SchedulerElement.ResizeBehavior.IsResizing)
                    {
                        this.Scheduler.SchedulerElement.ResizeBehavior.Resize(args.Location);
                    }
                    else if (appointment != null && IsRealDrag(args.Location))
                    {
                        this.Scheduler.Capture = false;
                        this.Scheduler.DragDropBehavior.BeginDrag((SchedulerVisualElement)appointment.Parent, appointment);
                        return true;
                    }
                }
                else
                {
                    if (appointment != null)
                    {
                        this.Scheduler.SchedulerElement.ResizeBehavior.RequestResize(appointment, (SchedulerVisualElement)appointment.Parent, false);
                    }
                    else
                    {
                        this.Scheduler.Cursor = Cursors.Default;
                    }
                }

                return false;
            }
            private void SelectCell(SchedulerCellElement cell, bool extend)
            {
                this.Scheduler.SelectionBehavior.SelectCell(cell, extend);
            }
        }

this.radScheduler1.SchedulerInputBehavior = new CustomSchedulerInputBheavior(this.radScheduler1);