Actually, the issue with reservations disappearing when waitlisted for an upgrade seems to have been resolved.
Originally Posted by bollar
aa.com does not display reservations that are on standby for an upgrade. Once the upgrade clears and you have confirmed that you actually want the upgrade, you'll be able to see the reservation again.
As for the taxes, you're a victim of a premium cabin tax. UK charges passengers in J or F more than coach passengers.