Alright i found the problem. It was in the rc.local file.
this line was automatically added when i installed my xbox controller :
#xboxdrv --daemon --id 1 --led 2 --deadzone 4000 --silent --trigger-as-button --next-controller --id 2 --led 3 --deadzone 4000 --silent --trigger-as-button --dbus disabled --detach-kernel-driv$
there’s something in that command that make my 2 xbox controllers ALWAYS present even if unplugged.
i replaced this line by
xboxdrv --trigger-as-button --id 1 --led 3 --deadzone 4000 --silent &
sleep 1
xboxdrv --trigger-as-button --id 2 --led 4 --deadzone 4000 --silent &
sleep 1
and now it works !!