Workaround: 
 Sub New()

        InitializeComponent()

        Me.SetUpGantt()

        Me.RadGanttView1.GanttViewElement.TextViewElement.Scroller.AllowHiddenScrolling = True

        AddHandler Me.RadGanttView1.MouseUp, AddressOf Me.RadGanttView1_MouseUp
    End Sub

Private Sub RadGanttView1_MouseUp(sender As Object, e As MouseEventArgs)
        Dim location = e.Location

        Dim splitter As GanttViewViewsSplitterElement = TryCast(Me.RadGanttView1.ElementTree.GetElementAtPoint(e.Location), GanttViewViewsSplitterElement)
        If splitter IsNot Nothing Then
            Me.RadGanttView1.GanttViewElement.TextViewElement.Scroller.Scrollbar.Value = Me.RadGanttView1.GanttViewElement.GraphicalViewElement.VScrollBar.Value
        End If
    End Sub