Becuase of a known vertical scrolling issue of the core DataGrid control that our GanttChartDataGrid control reuses, we have decided to disable the vertical scroll bar of the chart area (right side) to avoid any visual inconsistences between the thumb heights of the vertical scroll bars, while continuing to synchronize the actual positions of the left and right panes internally.
Although not recommended, if you need to re-enable the chart scroll bar it is possible to do so by setting IsChartVerticalScrollBarEnabled property of the GanttChartDataGrid control to true in your initialization code. Thank you for understanding.