I had the same thing happen on flights between LGA-DTW-HNL. The first flight was cancelled and I was rebooked by the computer on a flight that arrived in Detroit AFTER my connecting flight departed. There was no problem rebooking, although it was 3 hours earlier. The agent said the computer automatically chooses the flight closest in time to the one that was cancelled without looking at the rest of the record. Seems like they should update their software!