Possibly could be a clogged or damaged vent in the gas tank. Can be hard to find if it is. Might ask dealer if under warranty.
Does it take much after shutting off? If it is only a gallon or two it might be just the way it is. I have a Ford truck that will take a few gallons after shutting off but they all do. I think they design some room for compression to keep tank from rupturing in case of a crash.