A follow up to pgupta011 would be the example of where you had legitimately booked a 2 week trip somewhere months in advance then at the last minute a sale came up that let you go home for the weekend on short notice (webfares, e-fares etc.). Surely that wouldn't be back to back as the airlines would have to prove intent to circumvent the fare rules. All you would be doing was taking advantage of a last minute sale!