Gergely,
I think you hit the nail on the head. Although I am not a pilot, as I have mentioned in several other threads on this forum, I am in the IT industry and have worked on user interface designs for many years. I think overall the Airbus is a fine and safe line of airplanes, and their record proves that. Yet when I read through the descriptions of some of the incidents that have occurred, there seems to be a pattern of at least the possibility of a pilot not really understanding what was happening at the time of an incident. Let's use an analogy to discuss.
Suppose you own a high end passenger sedan. It has computer controlled handling characteristics which define their "modes" as primary and alternate law. In primary law, the amount of pressure you have to place on the accelerator is somewhat standard with other cars, as is the amount of pressure you need to place on the brakes to achieve a full stop. The steering characteristics are what would be described as "tight", meaning you do not have to move the steering wheel very far in order to achieve a relatively tight turn. In alternate law, all of these change. The amount of pedal pressure required for accelerating and braking double, as does the amount of steering wheel motion in order to achieve the same rate of turn as you would have had in normal law. The trigger to make the change from primary law to alternate law is a sensor which determines moisture on the road and the temperture of that moisture The change from primary to alternate is made so that you do not spin the wheels during acceleration, skid during decceleration, and you do not move too quickly into a turn and hence spin out. The indication to the driver that a change has been made from primary to alternate law (or back) is a combination of a chime and a light indicator on the dashboard.
Now, you are in your car driving with your wife beside you and two (or more) children in the back. The radio is on, and the kids are playing games. Suddenly a fight erupts in the back seat. It quickly escelates to a fever pitch. Your wife turns around and tries to stop it, but this only increases the noise in the car. At the same time, you drive into a summer thunderstorm, which quickly becomes a raging downpour mixed with hail. As the car progresses through the storm, the combination of rain (wet) mixed with hail (cold) meets the limits of acceptance for primary law, and the car switches to alternate law. You, on the other hand, are trying to calm the wife and kids down, while at the same time turning on the wipers and trying peer through the windscreen at the road. You turn back around one more time to try to settle the war as your wife screams; "You're missing the exit!". You immediately turn around, see the exit flying by, step on the brakes and turn the wheel. But, low and behold, you never heard the chime or saw the indicator light with all of the confusion. Suddenly the brakes aren't stopping the way you thought they were, and you can't get the car to turn into the exit. You're reaction isn't "the car must have changed modes", it is: "WTF is going on here??!!".
So after all of that, my point is, mode should not change without pilots concurrence, especially when it will effect how the controls react to input and what they will do with that input. If the pilot is assuming that limits are being controlled by the computer (especially where it pertains to rudder breakout or throttle settings), he may very quickly find himself further confused and with even less time to react. More importantly, he may further exacerbate the situation, if not cause damage to the aircraft.
In all of the design projects I have been on, we always focus on making sure the user interface remains constant so as to minimize confusion. If you cannot do that, then you should at least make the switch to those changes a conscious decision so that the person fully understands the implications, which may take a few seconds to recall and process. Otherwise you wind up with the "what is it doing now?" syndrome. And that is what worries me about how FBW is implemented.