Direwolf20 1.6.4 v1.0.0

2013-12-12 12:45:35 [INFO] [Minecraft-Server] An unknown error occurred while attempting to perform this command
2013-12-12 12:45:35 [INFO] [STDERR] java.lang.IllegalArgumentException: Comparison method violates its general contract!
2013-12-12 12:45:35 [INFO] [STDERR] 	at java.util.ComparableTimSort.mergeHi(ComparableTimSort.java:835)
2013-12-12 12:45:35 [INFO] [STDERR] 	at java.util.ComparableTimSort.mergeAt(ComparableTimSort.java:453)
2013-12-12 12:45:35 [INFO] [STDERR] 	at java.util.ComparableTimSort.mergeForceCollapse(ComparableTimSort.java:392)
2013-12-12 12:45:35 [INFO] [STDERR] 	at java.util.ComparableTimSort.sort(ComparableTimSort.java:191)
2013-12-12 12:45:35 [INFO] [STDERR] 	at java.util.ComparableTimSort.sort(ComparableTimSort.java:146)
2013-12-12 12:45:35 [INFO] [STDERR] 	at java.util.Arrays.sort(Arrays.java:472)
2013-12-12 12:45:35 [INFO] [STDERR] 	at java.util.Collections.sort(Collections.java:155)
2013-12-12 12:45:35 [INFO] [STDERR] 	at net.minecraft.command.CommandHelp.func_71534_d(SourceFile:74)
2013-12-12 12:45:35 [INFO] [STDERR] 	at net.minecraft.command.CommandHelp.func_71515_b(SourceFile:36)
2013-12-12 12:45:35 [INFO] [STDERR] 	at net.minecraft.command.CommandHandler.func_71556_a(CommandHandler.java:88)
2013-12-12 12:45:35 [INFO] [STDERR] 	at net.minecraft.server.dedicated.DedicatedServer.func_71333_ah(DedicatedServer.java:315)
2013-12-12 12:45:35 [INFO] [STDERR] 	at net.minecraft.server.dedicated.DedicatedServer.func_71190_q(DedicatedServer.java:277)
2013-12-12 12:45:35 [INFO] [STDERR] 	at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:587)
2013-12-12 12:45:35 [INFO] [STDERR] 	at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:484)
2013-12-12 12:45:35 [INFO] [STDERR] 	at net.minecraft.server.ThreadMinecraftServer.run(SourceFile:583)