I suspect that those who are most susceptible to moral proposition switches and their subsequent defense of switch, are also the same people that will deny the evidence when confronted with their switch. Much like the Dunning Kruger effect there will be people who fail to recognize the extremity of their inadequacy, even when confronted with evidence of such.

Edit: The paper states that they informed all participants of the true nature of the survey, but it does not go in to detail on whether participants actually acknowledged that their moral propositions were switched.