I had an interesting experience checking in online on Saturday for flying Sunday (yesterday). This might be common. I was in 8c and when I checked "seats" I saw that there was someone sitting in 8b next to me, even though the entire rest of the row was empty. "Eh?" I thought, and switched to 8d across the aisle. For an unrelated reason I looked at seats again before I printed my boarding passes, and found that the "person" had moved to 8e, next to me again! The light dawned, I switched to 8c and sure enough the "person" moved back. When I actually took the flight (ORD-YVR) 8b was empty on a mostly full flight. So I'm pretty sure that "person" was an automatic seat block. BTW pilot deadheading home ended up in 8a. I've had seats next to me blocked before but I've never seen this before in OLCI.