same thing happened to me on ORD-DTW......plane went from a 9F CR7 to a 6F CR7.....$300 voucher in my inbox by the time I landed on my inbound flight and a personal VM from EXP desk apologizing. I wasn't so luck with my coach seat assignment though as they couldn't give me my original MCE seat back or any exit row so I had to settle for a non-reclining regular Y seat.