To reproduce: please refer to the attached sample project. Try to edit the title for one of the child tasks in the grid and click the 

Workaround:

private void radGanttView1_ItemChanged(object sender, Telerik.WinControls.UI.GanttViewItemChangedEventArgs e)
{
    IEditableObject editebleObejct = e.Item.DataBoundItem as IEditableObject;
    if (editebleObejct != null)
    {
         editebleObejct.EndEdit();
    }
}