I want to be very clear about this: DO NOT TOUCH THE QUADSTICK WHILE IT IS POWERING UP.
If your lips were touching the mouthpiece AT ALL, the pressure sensor will be miscalibrated. Do not even exhale into the mouthpiece during power up.
Your answer did not explicitly indicate you understood this from my last message.
One way to test this is to power up the quadstick while no one is near it and let it sit there. If it activates on its own, there is a hardware problem and it will need to be repaired.