undo***redo не поддаются,что делать

If RichTextBox1.CanUndo = True Then
 
RichTextBox1.Undo()
 
RichTextBox1.ClearUndo()
End If

RichTextBox1.Redo()

RichTextBox1.Undo()

Dim keyCombo As New List(Of Keys)({Keys.ControlKey, Keys.D})
    Dim currentKeys As New List(Of Keys)
    Private Sub RichTextBox1_KeyDown(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles RichTextBox1.KeyDown
        currentKeys.Add(e.KeyCode)
        If currentKeys.Intersect(keyCombo).Count = keyCombo.Count Then
            If RichTextBox1.CanUndo = True Then
                RichTextBox1.Undo()
            ElseIf RichTextBox1.CanRedo = True Then
                RichTextBox1.Redo()
            End If
            currentKeys.Clear()
        End If
 
    End Sub
 
    Private Sub RichTextBox1_KeyUp(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles RichTextBox1.KeyUp
        currentKeys.Remove(e.KeyCode)
    End Sub
 
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        RichTextBox1.Undo()
    End Sub
 
    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        RichTextBox1.Redo()
    End Sub