upgrade hassles
Back in the days of Song and the one cabin configuration on some Delta planes, I had upgraded with miles on a coach ticket from Europe back home. Got to ATL and discovered that the final leg from ATL to ABQ was in coach. When I asked the GA, they told me that the plane was configured for coach only (it was a 737). When I complained after I got home about "paying" full freight for first class all the way, they said they were sorry but there was nothing that they could (or would) do about it. That was a very uncomfortable 3+ hours on that final leg.