<font face="Verdana, Arial, Helvetica, sans-serif" size="2">Originally posted by Old Gold:
Prior to EUA there was never a problem upgrading a segment of a 1 stop flight (with or without unscheduled change of aircraft)
Now, I don't know.</font>
No problem at all. Late last year, I was upgraded automatically on a flight from MSY to SAN, via IAH. Same flight number and same aircraft.