Thank you everybody for your answers.
Some remarks to help clear things :
"Richard you were at an altitude of 10574 when you requested an altitude change so that could be a factor as the altitude was rounded up. 11-2=9 more or less "
-The altimeter was in standard/1013mb but it would seem that PF3 not did not take into account. For reminder the zone where I fly (France) the transition height is of 4000ft (PF3 parameters).
-I have redo the same flight (logs attached) without putting the altimeter in 1013, this time the command "Lx" worked as hoped "L2"=-2000ft.
-But during the vectors approach, the control of approach left me in 8000ft or FL80. He has never asked me to descend.
-To finish, did the same flight again without asked to descend/cruise at FL80 and all worked like expected (descent, cap, speed and so on). This last flight is not in the Zip logs file.
Thanks and Regards,
Richard Portier