interesting. i realise that there must be much more evidence and study than is contained in that article, but it struck me that for the particular experiment they gave the people with the harder task may have a stronger sense of being "owed" something, since they made more effort, and that maybe this stronger sense of entitlement leads them to take more rewards...?
I will add that maybe some people felt not only 'owed' something but an urge for vengeance. The stricter test condition is not merely one requiring 'self control' but is rather draconian in the degree to which it requires self-control. There is a difference between expecting self-restraint and imposing hardship on people. "What goes around comes around". When you crap on people for purposes of your so-called experiments, don't be all shocked when they crap on you if given the opportunity.