Are we to assume that similar activities with software loads/configurations are conducted during ground testing; i.e. not flight worthy programs / configurations. If so then the problem is perhaps more with software control/configuration opposed to the design/operation of the power-plant control system, but the latter should never be discounted.
Most FADEC s/w has the ability to be 'trimmed' via a s/w adjustment. This trim capability is typically used during flight testing for specific testing - e.g. allowing a certain amount of overboost, or changing an idle schedule to facilitate some specific flight test objective. We have very specific processes and procedures on how these trims are used - for example if a trim is going to be used on all engines, it must be flight tested on a single engine first before it can be installed cross-wing. As I noted in the previous post - we are quite aware we're messing with flight critical s/w.
We had an incident in service a while back where a newly installed engine was squawked on the next flight for T/O thrust shortfall and excessive throttle stagger. The engine in question was a brand new spare received from the engine manufacture. It turned out that the engine manufacture used software trims in the engine test cell in order to perform some of the normal production acceptance testing on a new engine - and somehow this engine had gotten shipped with those s/w trims still installed in the FADEC
. Very embarrassing for the engine company, but fortunately there was a happy outcome, and new procedures were implemented to prevent a repeat.
Sorry for the speculation, but it rather sounds like some sort of s/w trim had been installed in the engine s/w (either by the engine manufacture, or by Airbus as part of their pre-flight functional testing) and not "removed prior to flight" on the three engines.