happens to me all the time. i've stopped bothering to confront them. i just find something more useful to indulge in. if all else fails good music through headphones and a great book can be an awesome distraction. let them be happy in thinking they got away with something.
i've discovered that some people cannot actually control their inconsistencies. they get most upset when they are faced with evidence of their cracked integrity. in fact it is a lot more fun trying to figure out where i may have probably got it wrong. i seldom find those, but it is so consuming that by the time i stop i had lost all interest in confrontation. it becomes just another academic exercise.