So this isn't the first time this has happened.

I was at the NWA I had shot a zombie oustide the NWA ATC and ran inside obviously the shot attracted more zombies. I had more than enough time to get inside, shut the door and then i made my way to the top floor and began to bandage myself. At which point i could here 5+ zombies outside scurrying around. All of a sudden a zombie started coming up the stairs into the control room and hit me once and i was dead.

This also happened to a friend of mine about 20 minute prior to this he had ran into one of the small green check point buildings shut the door and the zombie still got to him one hit killed.

In both of these occasions it was straight to YOU ARE DEAD!.

It seems like when the zombies have their momentum a door doesn't exist for them.