Excel: User-Defined Function nicht aktualisiert!?

' retrieve value from last non-empty row or column in selection
Function lastValue(rng As Range, searchRows As Boolean)
  Dim firstRow As Integer, firstCol As Integer, _
    rowCount As Integer, colCount As Integer, _
    i As Integer
 -> determine range
  firstRow = rng.Row
  firstCol = rng.Column
  rowCount = rng.rows.Count
  colCount = rng.Columns.Count
 -> default return value
  lastValue = CVErr(xlErrNA)
 -> search rows
  If searchRows = True Then
    For i = (firstRow + rowCount - 1) To firstRow Step -1
      If IsError(Cells(i, firstCol)) = False Then
        If Cells(i, firstCol).value <>  Then
          lastValue = Cells(i, firstCol).value
          Exit For
        End If
      End If
    Next i
 -> search columns
  Else
    For i = (firstCol + colCount - 1) To firstCol Step -1
      If IsError(Cells(firstRow, i)) = False Then
        If Cells(firstRow, i).value <>  Then
          lastValue = Cells(firstRow, i).value
          Exit For
        End If
      End If
    Next i
  End If
End Function

Option Explicit

Function LetzterWertImBereich2(myRange As Range, ByColumns As Boolean) As Variant

  Dim vonZeile As Long, bisZeile As Long
  Dim vonSpalte As Long, bisSpalte As Long
  Dim l_z As Long, l_sp As Long, x As Long
  Dim ws As Worksheet, r As Range

 ->Umfaßt Range nur ein Bereich ?
  If myRange.Areas.Count = 1 Then
    
   ->Worksheet setzen
    Set ws = myRange.Parent
    
   ->Range auf den Benutzten Bereich beschränken
    Set r = Intersect(myRange, ws.UsedRange)
    
   ->Anfangs-/Ende- / Zeile/Spalte
    vonZeile = r.Row
    bisZeile = r.Row + r.Rows.Count - 1
    vonSpalte = r.Column
    bisSpalte = r.Column + r.Columns.Count - 1
    
   ->Suchmodus
    If ByColumns Then
    
     ->letzte Zeile mit Wert suchen
      For l_z = bisZeile To vonZeile Step -1
        For l_sp = bisSpalte To vonSpalte Step -1
          With ws.Cells(l_z, l_sp)
           ->Fehlerwerte (#NV, ..) auslassen, da sonst <> auf die Nase fliegt
            If Not IsError(.Value) Then
              If .Value <>  Then LetzterWertImBereich2 = .Value: GoTo AUFRAEUMEN
            End If
          End With
        Next
      Next
      LetzterWertImBereich2 = CVErr(xlErrNA)
      
    Else
    
     ->letzte Spalte mit Wert suchen
      For l_sp = bisSpalte To vonSpalte Step -1
        For l_z = bisZeile To vonZeile Step -1
          With ws.Cells(l_z, l_sp)
           ->Fehlerwerte (#NV, ..) auslassen, da sonst <> auf die Nase fliegt
            If Not IsError(.Value) Then
              If .Value <>  Then LetzterWertImBereich2 = .Value: GoTo AUFRAEUMEN
            End If
          End With
        Next
      Next
      LetzterWertImBereich2 = CVErr(xlErrNA)
    End If
    
  Else
    LetzterWertImBereich2 = #MEHR_ALS_EIN_BEREICH
  End If
  
AUFRAEUMEN:
  Set ws = Nothing: Set r = Nothing
End Function

Private Sub Workbook_Open()
  Dim ws As Worksheet
  For Each ws In Worksheets
    ws.Cells.Replace What:==, Replacement:==, LookAt:=xlPart, SearchOrder _
      :=xlByRows, MatchCase:=False
  Next
End Sub

Private Sub Workbook_Open()
  Dim v As Variant, r As Range, r2 As Range
  Set r = Worksheets(1).Range(Worksheets(1).Cells(1, 1), Worksheets(1).Cells(1, 2))
  Set r2 = Worksheets(1).Range(Worksheets(1).Cells(3, 1), Worksheets(1).Cells(3, 2))
  v = LetzterWertImBereich2(Union(r, r2), False)
  Set r = Nothing
  Set r2 = Nothing
End Sub