TAdvDBLookupComboBox OnChange

I encountered a problem with TAdvDBLookupComboBox. The following code causes the item selection not to change

procedure TfrmInvoiceIncoming.addblucbMeasureUnit_041Change(Sender: TObject);
begin
  if dbdvdtPriceWithVAT_045.DataSource.DataSet.State in [dsEdit, dsInsert] then
    dbdvdtPriceWithVAT_045.DataSource.DataSet.FieldByName(dbdvdtPriceWithVAT_045.DataField).AsCurrency := 5;
end;

dbdvdtPriceWithVAT_045 is field in the main table. DataSource in TAdvDBLookupComboBox.