cla68:
What's behaviour is correct? is there a way to make the one locked moving "statically" ? Thanks
I assume neither of the servos is powered while you are trying to move them by hand.
Short of pushing harder and risking breaking the "locked" servo I have no idea what you can do.
However moving it manually won't make any difference to the Arduino. It will still go to the same place with Servo.write(90).
...R