The article totally glossed over how the long orders were "rolled over" from one trading period to the next. This seems like a critical detail. What happens when all the orders come due and you're holding a bunch of long orders? Also, wasn't this on HN a while ago? Or did I see it somewhere else?
(Aside: this is one reason why I have so little trust in the web as a long-term historical medium.)
Although that article focused primarily on oil futures, it also discussed commodities futures, and specifically addressed the rollovers. Unfortunately, I neither understood it well enough at the time, nor remember it well enough now, to regurgitate it. Maybe someone else will come along with a cached copy.