Definitely seems like a valid question.
I looked back through OU's last five seasons to see if there was any pattern (a high number or road games, a high number of rematches with other south teams, etc). I think six of those February losses came against teams OU had already played. I thought maybe teams/coaches "figured out" OU after the first game, but there's really no pattern with that, either (sometimes losing to teams you already beat, sometimes losing to teams you lost to already, sometimes simply splitting home and away).
I really don't see an explanation for it.