I've been told its a limitation of the Sabre booking engine full stop. It can only display a certain number of fare buckets on 1 screen so J cabin drops out. It's very shortsightedMay be they are doing this as safe guard against the scenario where people get upgraded at lounge and then downgraded at gate?
as customers dont readily get to see that sometimes the extra to travel J can be resonable trade up. Oh well they must know more about customer buying behaviour than anyone here.