Problem persists when server is set in either creative or survival. Zombies are not breaking down wooden doors at all. I have checked server.properties repeatedly. Game mode is set to hard, but the zombies still aren't breaking doors.

Server.Properties:
#Minecraft server properties
#Wed Jan 30 20:03:05 CST 2013
generator-settings=
allow-nether=true
level-name=FUNBUTT
enable-query=false
allow-flight=true
server-port=25565
level-type=DEFAULT
enable-rcon=false
level-seed=
server-ip=192.168.1.3
max-build-height=256
spawn-npcs=true
white-list=true
spawn-animals=true
snooper-enabled=true
hardcore=false
texture-pack=
online-mode=true
pvp=true
difficulty=3
enable-command-block=true
gamemode=0
max-players=6
spawn-monsters=true
generate-structures=true
view-distance=10
spawn-protection=0
motd=Cum and Have Funz