To my mind the most egregious example of out of order airing was in the 90s with the series American Gothic. There was clearly a lot of meddling with the show from the network and they wrote out a character who then inexplicably appears in another episode later in the season. They then released the DVDs in airing order as well.

Not that it's been the only case. Firefly only had 2 episodes out of order but as I recall there were several in Due South as well.