IF you are holding down the throttle and then the brake in that video, then it looks like you probably have a gamepad, joystick, steering wheel, or any other device also connected to the computer, and you didn't adjust the deadzones of this device. Try unplugging ALL devices except the keyboard. If you have configured mouse throttle / mouse brake, remove those bindings too. If you have installed 3rd party software that can create virtual input devices, or modify how input devices work in general, uninstall that too. Then try again to see if the issue disappeared