I'm absolutely sure I am not in peaceful mode I'll even provide my server properties at the end of this. I've tried switching between hard mode to peaceful and back again, nothing works. I've waited a few night, with no torches and far away from spawn points, no mobs spawn, not even in the caves. This is not a bukkit server and there are no mods or plugins. This has been happening since the recent 1.7.2 update and it's only in multiplayer server. If I play a in single player they'll spawn but if I transfer the world over to multiplayer all the mobs disappear. I can spawn mobs with a spawn egg but once you kill them they're gone. I've tried several different solutions from different forums but nothing helps.
#Minecraft server properties
#Wed Nov 20 10:50:50 PST 2013
generator-settings=
op-permission-level=4
allow-nether=true
level-name=world
enable-query=false
allow-flight=false
announce-player-achievements=true
server-port=25565
level-type=DEFAULT
enable-rcon=false
force-gamemode=false
level-seed=
server-ip=
max-build-height=256
spawn-npcs=true
white-list=false
spawn-animals=true
snooper-enabled=true
hardcore=false
online-mode=true
resource-pack=
pvp=true
difficulty=1
enable-command-block=false
player-idle-timeout=0
gamemode=0
max-players=5
spawn-monsters=true
view-distance=10
generate-structures=true
spawn-protection=1
motd=A Minecraft Server