How to reproduce: 
  this.radGanttView1.GanttViewElement.GraphicalViewElement.TimelineRange = Telerik.WinControls.UI.TimeRange.DayQuarterHours;
  this.radGanttView1.GanttViewElement.GraphicalViewElement.AutomaticTimelineTimeRange = true;
  this.radGanttView1.GanttViewElement.GraphicalViewElement.OnePixelTime = new TimeSpan(0, 0, 15);

Workaround: at the moment the Gantt control does not support an automatic timeline range for day quarter hours. The TimeRange.DayQuarterHours is similar to the half days and they should be handled the same way when in automatic timeline. If possible TimeRange.DayHalfHours 
this.radGanttView1.GanttViewElement.GraphicalViewElement.TimelineRange = Telerik.WinControls.UI.TimeRange.DayHalfHours;