Same problem that I am having.
Here's a more descriptive account of what's happening from my server console, from when I log in, up until I get disconnected:
17:46:53 [iNFO] SteelPhoenix [/x.xxx.xxx.xxx:xxxxx] logged in with entity id 362
at ([world] -229.86413064400142, 76.0, 190.63079796232952)
17:46:54 [iNFO] SteelPhoenix joined with mod_ModLoaderMp 1.1v4, mod_MinecraftFor
ge 1.3.3.12, mod_NotEnoughItems 1.1.1, mod_ReiMinimap v3.0_01 [1.1], mod_BuildCr
aftCore 2.2.12, mod_BuildCraftBuilders 2.2.12, mod_BuildCraftEnergy 2.2.12, mod_
BuildCraftFactory 2.2.12, mod_BuildCraftTransport 2.2.12, mod_IC2 v1.70, mod_Pow
erConverters 1.1.0R1.3.1, mod_RedPowerArray 2.0pr4d, mod_RedPowerCore 2.0pr4d, m
od_RedPowerLighting 2.0pr4d, mod_RedPowerLogic 2.0pr4d, mod_RedPowerMachine 2.0p
r4d, mod_RedPowerWiring 2.0pr4d, mod_RedPowerWorld 2.0pr4d, mod_Clevercraft 1.6.
2, mod_ItemDescriptions 1.3, mod_EnderChest 1.0.1, mod_Forestry 1.2.6.4, mod_zAd
ditionalPipes Rev32.3, mod_ComputerCraft 1.21, mod_EE EE2 v1.0.0, mod_InvTweaks
1.38 (1.1), mod_MAtmos_forModLoader r10 for 1.1.x, mod_NetherOres 1.1.0R1.1.2, m
od_RailcraftAutomation 3.3.1, mod_RailcraftBuildcraft 3.3.1, mod_RailcraftCore 3
.3.1, mod_RailcraftExtras 3.3.1, mod_RailcraftFactory 3.3.1, mod_RailcraftIC2 3.
3.1, mod_RailcraftInfrastructure 3.3.1, mod_RailcraftRails 3.3.1
17:46:54 [iNFO] SteelPhoenix joined with mod_ModLoaderMp 1.1v4, mod_MinecraftFor
ge 1.3.3.12, mod_NotEnoughItems 1.1.1, mod_ReiMinimap v3.0_01 [1.1], mod_BuildCr
aftCore 2.2.12, mod_BuildCraftBuilders 2.2.12, mod_BuildCraftEnergy 2.2.12, mod_
BuildCraftFactory 2.2.12, mod_BuildCraftTransport 2.2.12, mod_IC2 v1.70, mod_Pow
erConverters 1.1.0R1.3.1, mod_RedPowerArray 2.0pr4d, mod_RedPowerCore 2.0pr4d, m
od_RedPowerLighting 2.0pr4d, mod_RedPowerLogic 2.0pr4d, mod_RedPowerMachine 2.0p
r4d, mod_RedPowerWiring 2.0pr4d, mod_RedPowerWorld 2.0pr4d, mod_Clevercraft 1.6.
2, mod_ItemDescriptions 1.3, mod_EnderChest 1.0.1, mod_Forestry 1.2.6.4, mod_zAd
ditionalPipes Rev32.3, mod_ComputerCraft 1.21, mod_EE EE2 v1.0.0, mod_InvTweaks
1.38 (1.1), mod_MAtmos_forModLoader r10 for 1.1.x, mod_NetherOres 1.1.0R1.1.2, m
od_RailcraftAutomation 3.3.1, mod_RailcraftBuildcraft 3.3.1, mod_RailcraftCore 3
.3.1, mod_RailcraftExtras 3.3.1, mod_RailcraftFactory 3.3.1, mod_RailcraftIC2 3.
3.1, mod_RailcraftInfrastructure 3.3.1, mod_RailcraftRails 3.3.1
17:47:13 [WARNING] Failed to handle packet: java.lang.IndexOutOfBoundsException:
Index: 71, Size: 45
java.lang.IndexOutOfBoundsException: Index: 71, Size: 45
at java.util.ArrayList.RangeCheck(Unknown Source)
at java.util.ArrayList.get(Unknown Source)
at net.minecraft.server.Container.a(SourceFile:128)
at net.minecraft.server.NetServerHandler.a(NetServerHandler.java:997)
at net.minecraft.server.Packet102WindowClick.handle(SourceFile:28)
at net.minecraft.server.NetworkManager.b(NetworkManager.java:231)
at net.minecraft.server.NetServerHandler.a(NetServerHandler.java:101)
at net.minecraft.server.NetworkListenThread.a(NetworkListenThread.java:7
8)
at net.minecraft.server.MinecraftServer.w(MinecraftServer.java:543)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:441)
at net.minecraft.server.ThreadServerApplication.run(SourceFile:465)
I got disconnected when clicking on my hot bar. Wondering if a lot of people are having this problem in creative mode?