I have a basic report:

<?php
class OrdersWithLineItems extends SS_Report
{
  public function title()
  {
    return 'Orders with Line Items';
  }

  public function sourceRecords($params, $sort, $limit)
  {
    $ordersAL = new ArrayList();

    $OrderHeaders = OrderHeader::get();

    foreach ($OrderHeaders as $OrderHeader) {
      foreach ($OrderHeader->OrderItems() as $OrderItem) {
        $tempOrderHeader = new DataObject($OrderHeader->toMap());

        $tempOrderHeader->ProductCode     = $OrderItem->Product()->PartNumber;
        $tempOrderHeader->ProductQuantity = $OrderItem->Quantity;

        $ordersAL->add($tempOrderHeader);
      }
    }

    return $ordersAL;
  }


  public function columns()
  {
    $fields = array(
      'StripeID' => array(
        'title' => 'StripeID',
        'link' => false
      ),
      'OrderTotal' => array(
        'title' => 'OrderTotal',
        'link' => false
      ),
      'SalesTax' => array(
        'title' => 'SalesTax',
        'link' => false
      ),
      'SalesTaxCity' => array(
        'title' => 'SalesTaxCity',
        'link' => false
      ),
      'SalesTaxState' => array(
        'title' => 'SalesTaxState',
        'link' => false
      ),
      'SalesTaxZip' => array(
        'title' => 'SalesTaxZip',
        'link' => false
      ),
      'OrderComplete' => array(
        'title' => 'OrderComplete',
        'link' => false
      ),
      'Email' => array(
        'title' => 'Email',
        'link' => false
      ),
      'PromoCode' => array(
        'title' => 'PromoCode',
        'link' => false
      ),
      'BillingName' => array(
        'title' => 'BillingName',
        'link' => false
      ),
      'BillingAddress1' => array(
        'title' => 'BillingAddress1',
        'link' => false
      ),
      'BillingAddress2' => array(
        'title' => 'BillingAddress2',
        'link' => false
      ),
      'BillingCity' => array(
        'title' => 'BillingCity',
        'link' => false
      ),
      'BillingState' => array(
        'title' => 'BillingState',
        'link' => false
      ),
      'BillingZip' => array(
        'title' => 'BillingZip',
        'link' => false
      ),
      'ShippingName' => array(
        'title' => 'ShippingName',
        'link' => false
      ),
      'ShippingAddress1' => array(
        'title' => 'ShippingAddress1',
        'link' => false
      ),
      'ShippingAddress2' => array(
        'title' => 'ShippingAddress2',
        'link' => false
      ),
      'ShippingCity' => array(
        'title' => 'ShippingCity',
        'link' => false
      ),
      'ShippingState' => array(
        'title' => 'ShippingState',
        'link' => false
      ),
      'ShippingZip' => array(
        'title' => 'ShippingZip',
        'link' => false
      ),
      'ProductCode' => array(
        'title' => 'ProductCode',
        'link' => false
      ),
      'ProductQuantity' => array(
        'title' => 'ProductQuantity',
        'link' => false
      )
    );

    return $fields;
  }
}

Which works as expected in the browser, but when attempting to download I only get the column headers and blank rows. The number of rows is the same number as the records that are missing, but no data. Any ideas? And I going about building this report, with related (has_many) DataObjects incorrectly?

Thanks and Regards,
Todd M. Kimball