That's strange, Smash controllers aren't supposed to have this kind of issues. You should ask for a replacement.
I will, thanks, but from what I see it's a common issue with the smash controllers actually
I download version 5.0-9863, and it fixed the issue for me completely, all of my games are now perfectly playable with the controller (Even though the triggers themselves do always register as being pressed according to the windows calibration tool in PC mode).
Be careful not to touch the triggers when booting a game. They're analog, like the analog stick, so at booting time, their current position are defined as the neutral position.
We recently fixed a regression with the GameCube Controller + running multiple games which is probably what was going on.