Originally Posted by
JY1024
That explanation certainly make sense. If the AAgents/computer system already upgraded you from Y->F and Y is now completely full, then the "un-upgrade" wouldn't be possible...
Not so much the cabin being full as the fare class originally purchased being unavailable to return to. I suppose one could always pay the fare difference to full Y, but that would almost certainly cost more than the stickers to say in F. Seems a no brainer.
In the case of the flight I was on, the Y cabin was in fact not full, but nevertheless I was not allowed to downgrade.