Ballooning, speed trends, pitch changes - this is just a normal characteristic of every jet airliner.
Airbus never intended to overcome these effects by the flight guidance. One of its golden rules (actually the first one) states that:
"Inspite of FBW, the aircraft can be flown like any other aircraft."
It is not advisable to take the pilot out of the loop by diminshing aerodynamic effects. So there will always be a ballooning, not only, but very pronounced, when selecting flaps 2 (the biggest change of lift on flap changes).
hth,
Dani