sectionNameKeyPath with NSFetchedResultsController not working

I have an entity Order with property paid, which is a boolean.

I want to display all orders in a UITableView, but I want to group them in two sections: 'Not Paid' and 'Paid'. So I thought I'd just give "paid" as sectionNameKeyPath, like this:

fetchedResultsController = [[NSFetchedResultsController alloc]
         initWithFetchRequest:fetchRequest
         managedObjectContext:managedObjectContext
           sectionNameKeyPath:@"paid"
                    cacheName:nil];

According to my reasoning, this would result in two sections, where the first section contains all orders with paid = NO (0) and the second section with paid = YES (1).

But when I add a new Order with paid = YES, it shows up in the first section. When I check in the fetched results controller delegate, I can see that a new record with indexPath [0,0] is created! Why doesn't it get inserted in the second section?