I'm in the "pier" level I think -- past the hang glider where you sneak through the jungle and get to a little base with barracks, guards, jeeps, helicopter, etc and have to blow up some ammunition. Anyway, as soon as they detect me everyone starts firing at me constantly even when I'm inside a building or behind cover -- the bullets just sail through right at me. Even the enemy jeep at the other end of the base, which normally bursts out once you start diving away, sits there firing its rail gun right through the wall all the way across at my position.
This didn't happen at all to this point, so what's up? I can beat it by playing cheap and drawing guards in a line into the jungle but I'd rather play for real.