How to reproduce: Make sure that the StartDate of the current view is not the first day of the week. Change the view to timeline and set the time scale to be Weeks:
this.radScheduler1.ActiveViewType = SchedulerViewType.Timeline;
SchedulerTimelineView view = this.radScheduler1.GetTimelineView();
view.ShowTimescale(Timescales.Weeks);
Workaround:
Change the view`s start day to the first day of the week before changing the scale:
this.radScheduler1.ActiveViewType = SchedulerViewType.Timeline;
SchedulerTimelineView view = this.radScheduler1.GetTimelineView();
DateTime date = DateHelper.GetStartOfWeek(view.StartDate, view.CurrentCulture.DateTimeFormat);
view.StartDate = date;
view.ShowTimescale(Timescales.Weeks);