t just work with the 1M ohm resistor.. but just for a millisecond
Yes that is how those sensors are supposed to work. I think you are expecting then to do something else. They are not touch sensors you get a very quick spike when they experience a mechanical shock.
You could try a small capacitor across the sensors like a 0.1uF to extend the pulse but you are better off extending it in software.
but the Serial.print write down something strange:
Yes that is exactly why you are seeing the light behave like you are. As I said before you have a floating input and that means it could pick up anything.