Admin area has different $context array for hook_uc_price_handler than "client" area

This issue is related to this one #488652: calculate_product_discounts not triggered when adding products from admin area in UC Discount Framework module. It might also be related to #475474: Price alterer contexts and VAT support.
The problem is that when adding an order from the Admin area you can't get a $node from the $context array of the hook_uc_price_handler callback function.
For example when adding an order from the admin area the following code (copy-pasted from UC Discount Framework) will always get to the 3rd if ("// Nothing to do." bit):

/**
 * Implementation of hook_uc_price_handler().
 */
function uc_discount_uc_price_handler() {
  return array(
    'alter' => array(
      'title' => t('Discount price handler'),
      'description' => t('Adds discounts to product prices.'),
      'callback' => 'uc_discount_price_handler_alter',
    ),
  );
}

function uc_discount_price_handler_alter(&$price_info, &$context, &$options) {
  global $user;
  static $prices = array('node_prices' => array(), 'cart_prices' => array());

  if (isset($context['subject']['node']) && (!isset($context['subject']['field']) || $context['subject']['field'] == 'sell_price')) {
    $node = $context['subject']['node'];
    $cache = 'node_prices';
  }
  else if (isset($context['extras']['node']) && isset($context['subject']['cart_item'])) {
    $node = clone $context['extras']['node'];
    $item = $context['subject']['cart_item'];
    if (isset($context['subject']['field']) && isset($item->{$context['subject']['field']})) {
      $node->sell_price = $item->{$context['subject']['field']};
    }
    else {
      $node->sell_price = $item->price;
    }
    $cache = 'cart_prices';
  }
  else {
    // Nothing to do.
    return;
  }