I was once on a DFW/SFO/ORD/FRA run. Before landing in SFO, the FA came on the intercom and stated that she was sure this was a mistake, but if anyone was connecting to ORD to please ring the call button. I rang my call button and she approached. All I said was "it's a mileage run." She gave me connecting gate info and said that even the captain said that "this MUST be a mistake."