When 307 gasoline is low, it is pressing the gas ??

I have 2004 307 1.6 xt premium.
It seems that gasoline is decreasing while the vehicle is going with LPG, but it is a normal thing, but when the gas light is on, when you try to stop in the light or want to park, the car presses the gas and you have to hang on the brake. What is this problem?