Problem in copying Excel sheet with VBA formula

I have a workbook with a number of similar sheets in which some cells contain a VBA formula, i.e. =newValue() . When I try to copy one of those sheets e.g. at the end of the same workbook, using the "Move or copy sheet" tab, the copy is done OK, but in ALL the other sheets, the value in the formula cells duplicate the values from the copied sheet. If I look at the contents of such a wrongly-duplicated cells, it shows the formula name, and not the value. This problem exists in Excel 2007 and Excel 2013. What shall be done to overcome the problem?

Here are relevant excerpts of the VBA code:

Function newValue()         'newValue(depCells)
    
    curRow = Application.ThisCell.Row
    curCol = Application.ThisCell.Column
    curOp = Cells(curRow, 2).Value
    
    If curCol = 4 Then
        lastVal = Cells(lastRow, 4).Value
        If curOp = "B" Then
            newValue = lastVal + Cells(curRow, 3).Value
        ElseIf curOp = "S" Then
            newValue = lastVal - Cells(curRow, 3).Value
        Else
            newValue = ""
        End If
   
    ElseIf curCol = 6 Then  ...

    End If
    
End Function