Experienced this yesterday on ORD-SFO. I was confirmed in row 3, everything was fine a couple days before the flight, when I went to check in I found I had been dumped into a seat way in the back of the plane. I think this was a row renumbering issue, as the announcements identified row 6 as the bulkhead. The flight was fine, and while I prefer to sit further up, it's really only a difference of a few minutes waiting to get off the plane, but this was all handled without any sort of notice or supporting information. It also seemed to mess up my boarding pass, as I wasn't assigned a boarding group (also not a big deal, but it further gives the impression that this is a really confused transition).