[PHXFlyer]

Did you check-in online? During online check in on Continental if there is available space on an earlier or later flight it will give you those options. Could something have gone wrong? If you did check in online do you remember seeing this?

Another question if I may. Was your wife's reservation under the same original confirmation as yours?

It could also be that the earlier flight was overbooked and there were some shenanigans going on behind the scenes to move you and possibly others to the later flight. Were there any others on the earlier flight that suddenly found themselves on the later one? This should be reported to Continental and as The_Judge said there is an electronic "paper trail" that can be followed to determine exactly when it was changed and by whom.