There's not a great deal u can do about this on Spyders - the gas has to push the bolt back and recock the gun as well as fire the ball, so as the bolt moves backwards, there is still gas coming from it. Naturally, some of it goes up the feedneck.
Some Spyders have an angled-feed body that have a vent on the side that allows this gas to escape, and the angle helps prevent the gas from blowing the balls back around the bend.