Left 4 Dead

When I was playing my left 4 dead 1 game. I was over at my mga kaibigan playing left 4 dead. he was playing resident evil 5 on his game and I was playing left 4 dead with his little brother. We were about to play campian. Then all sudden it showed 'Last Stand' it was impossible! 'last stand' is only in survival mode. Its never on campian mode whatsoever. I started it cause I wanted to investigate. You spawn at the back of the frence sa pamamagitan ng the light house. But the background, you can go through it, but it looked like cardboard but the back of it theres nothing. I found some infected zombies. Well some...