Myself and a friend were on a morning Aeroflot flight from Tashkent to Moscow, which I recall being an A321. Anyway, we were about the first to board (as I'd rightly assessed that it would be utterly chaotic) and took our allocated seats behind the second bulkhead in economy.
After a bit an Uzbek passenger said we were in his seats, so i got my ticket out and politely told him we were in our seats. So off he went to speak to an attendant who ultimately plonked him at elsewhere in the cabin. Then a few minutes later a Russian passenger came along and the same process ensued.
When the flight had finished loading and all passengers were seated, an attendant came up, asked for our tickets and went off to the front. Few minutes later she returned with new tickets, apologised for the over-full flight and said that we were being upgraded to business. Not entirely sure why we were singled out, particularly as everyone seemed to be sorted out seat-wise. Anyway, we were quite happy to take the wider seats, extra legroom and proper meals.