Index: commerce_cart.module
===================================================================
--- cart/commerce_cart.module   (revision 471)
+++ commerce_cart.module   (working copy)
@@ -401,7 +401,8 @@
 
   // Reference the current shopping cart order in the line item if it isn't set.
   if (empty($line_item->order_id)) {
-    $line_item->order_id = commerce_cart_order_id($user->uid);
+    $order = commerce_cart_order_load($user->uid);
+    $line_item->order_id = $order->order_id;
   }
 }