1.4.6 to 1.4.7 error? Investigate.

Hello Bukkit! I'm having an error when a 1.4.6 client is connecting to my 1.4.7 server. This is obviously STRANGE, because both you and Mojang report that there shouldn't be any any errors. However, THIS appears in my log.
[INFO] Disconnecting thisusername [/x.x.x.x:58068]: Internal server error
[WARNING] Failed to handle packet for thisusername [/x.x.x.x:58068]: java.lang.NullPointerException
java.lang.NullPointerException
at net.minecraft.server.v1_4_6.PlayerList.attemptLogin(PlayerList.java:239)
at net.minecraft.server.v1_4_6.PendingConnection.d(PendingConnection.java:121)
at net.minecraft.server.v1_4_6.PendingConnection.c(PendingConnection.java:45)
at net.minecraft.server.v1_4_6.DedicatedServerConnectionThread.a(DedicatedServerConnectionThread.java:44)
at net.minecraft.server.v1_4_6.DedicatedServerConnection.b(SourceFile:29)
at net.minecraft.server.v1_4_6.MinecraftServer.r(MinecraftServer.java:598)
at net.minecraft.server.v1_4_6.DedicatedServer.r(DedicatedServer.java:224)
at net.minecraft.server.v1_4_6.MinecraftServer.q(MinecraftServer.java:494)
at net.minecraft.server.v1_4_6.MinecraftServer.run(MinecraftServer.java:427)
at net.minecraft.server.v1_4_6.ThreadServerApplication.run(SourceFile:849)
But this isn't a critical error, and doesn't crash my server. But I still wonder... Any help?

 

Try removing all your plugins?
Update to the latest build?

 

Why didn't the player update to 1.4.7? Maybe they have a heavily modded client?

 

I'm not even sure, .... Perhaps they forgot. But I know their client is modded, so I guess a conflict? Still, an odd error...