[MC-827] Server Crash when client logs in with invalid difficulty

The server (privately hosted on my PC and have had no issues in previous versions) crashes within seconds upon any user logging into it without fail since the 1.4.2 version of the client and server have been updated.

This happens in a brand new world/seed and in our existing seeds/worlds from previous versions.

Server log generates the following:

SEVERE] Encountered an unexpected exception ArrayIndexOutOfBoundsException
java.lang.ArrayIndexOutOfBoundsException: 4
	at qa.bD(SourceFile:261)
	at xr.a(SourceFile:162)
	at xr.a(SourceFile:139)
	at ie.b(SourceFile:106)
	at net.minecraft.server.MinecraftServer.r(SourceFile:717)
	at hg.r(SourceFile:233)
	at net.minecraft.server.MinecraftServer.q(SourceFile:661)
	at net.minecraft.server.MinecraftServer.run(SourceFile:595)
	at fp.run(SourceFile:818)
[SEVERE] This crash report has been saved to: D:\Minecraft\1.4.2 Server\.\crash-reports\crash-2012-10-26_18.03.47-server.txt

See attached crash report for further information. Apologies if this is a repeat issue, I did briefly scan the other issue titles.