i live in Toulouse too, i have an EasyStar too and the same problem!
But i can not explain what...
I have built eight EZ*s and crashed four of them beyond repair. All of my present EZ*s have brushless motors, big rudders, and ailerons.
Depending on the size of your brushless motor, you may have a brushless motor that is overpowering your EZ*. I presently use both inrunner and outrunner brushless motors of around 2200kv and ~200-250watts. The more powerful the motor, the bigger the rudder.
Also, I have reinforced the fuse with carbon fiber rods from tail to nose including the wing shoulder.
The EZ* will plow nose down if you only use the rudder to turn. You need to have some up elevator during a turn. Installing ailerons on your EZ* or buying an EZ* II is the best way to go. The EZ* equipped with ailerons is a joy to fly. Also you might want to consider installing a CoPilot II to help you learn to fly well.
Just a thought.