Microsoft Dynamics Navision - Creating Production BOM line using Web Services

Im trying to create Production BOM lines using web services. I can construct the lines fine, but as soon as i update the ProdBOMLine() is set back to 0. I have used this code on other Nav integrations but on this one it doesn't like it. I cant figure out what could be different.

Public Sub CreateBOM(BomNo As String, Description As String, UOM As String, 
bomLines As List(Of Object()))

    Dim bom As New Integration_Production_BOM()
    bom.No = BomNo
    bom.Description = Description
    bom.Unit_of_Measure_Code = UOM
    bomService.Create(bom)

    lastReadBOM = bom
    AddBomLines(lastReadBOM, bomLines)

    lastReadBOM.Status = NAV_Bom.Status.Certified
    bomService.Update(lastReadBOM)

End Sub

Private Sub AddBomLines(ByRef bom As Integration_Production_BOM, bomLines As List(Of Object()))

    bom.ProdBOMLine = New Integration_Production_BOM_Lines(bomLines.Count - 1) {}

    For i As Integer = 0 To bomLines.Count - 1
        bom.ProdBOMLine(i) = New Integration_Production_BOM_Lines()
    Next
    ' bomService.Update(bom)

    Dim position As Integer = 0

    For Each bomLine As Object() In bomLines

        If bomLine(0) = True Then
            bom.ProdBOMLine(position).Type = NAV_Bom.Type.Production_BOM
        Else
            bom.ProdBOMLine(position).Type = NAV_Bom.Type.Item
        End If

        bom.ProdBOMLine(position).No = bomLine(1)
        bom.ProdBOMLine(position).Quantity_per = bomLine(2)
        bom.ProdBOMLine(position).Description = bomLine(4)

        If Not String.IsNullOrEmpty(bomLine(3)) Then
            bom.ProdBOMLine(position).Variant_Code = bomLine(3)
        End If

        position += 1
    Next
    '''Here bom.ProdBOMLine.Count = 3
    bomService.Update(bom)
    '''Here bom.ProdBOMLine.Count = 0
End Sub