This is true, however, it may be that LNF changes are processed differently and do not cause the tracking to break. If your reservation # changes, I'm almost sure that will cause cash back to not post... but LNF might be implemented while leaving that information alone. You don't, for example, want to call Marriott and say, "I'd like to change my current reservation to the AAA rate because it is 2% lower than what I have now"... that would cause them to essentially cancel and rebook, in which case you'd lose the 3%+ cash back (you'd want to cancel online and rebook via the cash back link again, instead). In other words, changing your rate code or confirmation # is probably what causes the break, but simply having a credit processed might not.