Updated mcmmo version breaks public messages being sent to IRC. Remove or downgrade mcmmo and the problem goes away. Here is the error:

2013-02-19 14:16:47 [SEVERE] Could not pass event AsyncPlayerChatEvent to MonsterIRC v1.72
org.bukkit.event.EventException
at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:427)
at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:62)
at org.bukkit.plugin.SimplePluginManager.fireEvent(SimplePluginManager.java:477)
at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:459)
at net.minecraft.server.v1_4_R1.PlayerConnection.chat(PlayerConnection.java:903)
at net.minecraft.server.v1_4_R1.PlayerConnection.a(PlayerConnection.java:853)
at net.minecraft.server.v1_4_R1.Packet3Chat.handle(Packet3Chat.java:44)
at net.minecraft.server.v1_4_R1.Packet3Chat$$EnhancerByCGLIB$$52b93fb.CGLIB$handle$0()
at net.minecraft.server.v1_4_R1.Packet3Chat$$EnhancerByCGLIB$$52b93fb$$FastClassByCGLIB$$f8b8027f.invoke()
at com.comphenix.net.sf.cglib.proxy.MethodProxy.invokeSuper(MethodProxy.java:228)
at com.comphenix.protocol.injector.packet.ReadPacketModifier.intercept(ReadPacketModifier.java:109)
at net.minecraft.server.v1_4_R1.Packet3Chat$$EnhancerByCGLIB$$52b93fb.handle()
at net.minecraft.server.v1_4_R1.NetworkManager.i(NetworkManager.java:208)
at net.minecraft.server.v1_4_R1.NetworkManager.c(NetworkManager.java:344)
at net.minecraft.server.v1_4_R1.NetworkReaderThread.run(SourceFile:93)
Caused by: java.lang.NoSuchMethodError: com.gmail.nossr50.datatypes.PlayerProfile.getAdminChatMode()Z
at org.monstercraft.irc.plugin.managers.listeners.MonsterIRCListener.onChat(MonsterIRCListener.java:62)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:425)
... 14 more

I already submitted a pull request to fix this. I'm not sure when the plugin author will actually release the updated version on Bukkit Dev....