Hopper: java.lang.RuntimeException: Already decorating!!

This is an automatically generated report based from the following crash: http://hopper.minecraft.net/crashes/minecraft/MCX-53300/

Crash:

java.lang.RuntimeException: Already decorating!!
	at act.a(SourceFile:21)
	at acp.a(SourceFile:217)
	at acw.a(SourceFile:21)
	at aen.a(SourceFile:155)
	at jq.a(SourceFile:168)
	at adq.a(SourceFile:732)
	at jq.c(SourceFile:105)
	at jq.d(SourceFile:116)
	at abv.e(SourceFile:289)
	at ack.<init>(SourceFile:32)
	at abv.a(SourceFile:2222)
	at re.a(SourceFile:88)
	at pz.a(SourceFile:38)
	at ps.a(SourceFile:67)
	at of.bh(SourceFile:410)
	at oe.c(SourceFile:1289)
	at of.c(SourceFile:292)
	at tl.c(SourceFile:24)
	at tv.c(SourceFile:141)
	at oe.l_(SourceFile:1176)
	at of.l_(SourceFile:169)
	at tl.l_(SourceFile:29)
	at tv.l_(SourceFile:197)
	at abv.a(SourceFile:1349)
	at jr.a(SourceFile:479)
	at abv.g(SourceFile:1327)

The following is the first clean report made public about this crash:

---- Minecraft Crash Report ----
// Why is it breaking :(

Time: 09/08/13 16:29
Description: Ticking entity

java.lang.RuntimeException: Already decorating!!
	at act.a(SourceFile:21)
	at acp.a(SourceFile:217)
	at acw.a(SourceFile:21)
	at aen.a(SourceFile:155)
	at jq.a(SourceFile:168)
	at adq.a(SourceFile:732)
	at jq.c(SourceFile:105)
	at jq.d(SourceFile:116)
	at abv.e(SourceFile:289)
	at ack.<init>(SourceFile:32)
	at abv.a(SourceFile:2222)
	at re.a(SourceFile:88)
	at pz.a(SourceFile:38)
	at ps.a(SourceFile:67)
	at of.bh(SourceFile:410)
	at oe.c(SourceFile:1289)
	at of.c(SourceFile:292)
	at tl.c(SourceFile:24)
	at tv.c(SourceFile:141)
	at oe.l_(SourceFile:1176)
	at of.l_(SourceFile:169)
	at tl.l_(SourceFile:29)
	at tv.l_(SourceFile:197)
	at abv.a(SourceFile:1349)
	at jr.a(SourceFile:479)
	at abv.g(SourceFile:1327)
	at abv.h(SourceFile:1234)
	at jr.h(SourceFile:364)
	at net.minecraft.server.MinecraftServer.t(SourceFile:470)
	at net.minecraft.server.MinecraftServer.s(SourceFile:405)
	at bkw.s(SourceFile:124)
	at net.minecraft.server.MinecraftServer.run(SourceFile:339)
	at hh.run(SourceFile:582)


A detailed walkthrough of the error, its code path and all known details is as follows:
---------------------------------------------------------------------------------------

-- Head --
Stacktrace:
	at act.a(SourceFile:21)
	at acp.a(SourceFile:217)
	at acw.a(SourceFile:21)
	at aen.a(SourceFile:155)
	at jq.a(SourceFile:168)
	at adq.a(SourceFile:732)
	at jq.c(SourceFile:105)
	at jq.d(SourceFile:116)
	at abv.e(SourceFile:289)
	at ack.<init>(SourceFile:32)
	at abv.a(SourceFile:2222)
	at re.a(SourceFile:88)
	at pz.a(SourceFile:38)
	at ps.a(SourceFile:67)
	at of.bh(SourceFile:410)
	at oe.c(SourceFile:1289)
	at of.c(SourceFile:292)
	at tl.c(SourceFile:24)
	at tv.c(SourceFile:141)
	at oe.l_(SourceFile:1176)
	at of.l_(SourceFile:169)
	at tl.l_(SourceFile:29)
	at tv.l_(SourceFile:197)
	at abv.a(SourceFile:1349)
	at jr.a(SourceFile:479)
	at abv.g(SourceFile:1327)

-- Entity being ticked --
Details:
	Entity Type: Zombie (tv)
	Entity ID: 298
	Entity Name: Zombie
	Entity's Exact location: -41.31, 236.00, 80.68
	Entity's Block location: World: (-42,236,80), Chunk: (at 6,14,0 in -3,5; contains blocks -48,0,80 to -33,255,95), Region: (-1,0; contains chunks -32,0 to -1,31, blocks -512,0,0 to -1,255,511)
	Entity's Momentum: 0.00, -0.08, 0.00
Stacktrace:
	at abv.h(SourceFile:1234)
	at jr.h(SourceFile:364)

-- Affected level --
Details:
	Level name: Flat!
	All players: 0 total; []
	Chunk stats: ServerChunkCache: 755 Drop: 0
	Level seed: 7286781567508412194
	Level generator: ID 01 - flat, ver 0. Features enabled: true
	Level generator options: 2;7,230x1,5x3,2;3;stronghold,biome_1,decoration,dungeon,mineshaft
	Level spawn location: World: (0,4,0), Chunk: (at 0,0,0 in 0,0; contains blocks 0,0,0 to 15,255,15), Region: (0,0; contains chunks 0,0 to 31,31, blocks 0,0,0 to 511,255,511)
	Level time: 3733 game time, 3733 day time
	Level dimension: 0
	Level storage version: 0x04ABD - Anvil
	Level weather: Rain time: 129980 (now: false), thunder time: 74456 (now: false)
	Level game mode: Game mode: creative (ID 1). Hardcore: false. Cheats: true
Stacktrace:
	at net.minecraft.server.MinecraftServer.t(SourceFile:470)
	at net.minecraft.server.MinecraftServer.s(SourceFile:405)
	at bkw.s(SourceFile:124)
	at net.minecraft.server.MinecraftServer.run(SourceFile:339)
	at hh.run(SourceFile:582)

-- System Details --
Details:
	Minecraft Version: 1.6.2
	Operating System: Windows 8 (x86) version 6.2
	Java Version: 1.7.0_25, Oracle Corporation
	Java VM Version: Java HotSpot(TM) Client VM (mixed mode, sharing), Oracle Corporation
	Memory: 9983928 bytes (9 MB) / 518979584 bytes (494 MB) up to 518979584 bytes (494 MB)
	JVM Flags: 2 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx512M
	AABB Pool Size: 405 (22680 bytes; 0 MB) allocated, 405 (22680 bytes; 0 MB) used
	Suspicious classes: No suspicious classes found.
	IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: 52 (2912 bytes; 0 MB) allocated, 52 (2912 bytes; 0 MB) used
	Player Count: 0 / 8; []
	Type: Integrated Server (map_client.txt)
	Is Modded: Probably not. Jar signature remains and both client + server brands are untouched.

You can see this full report at http://hopper.minecraft.net/crashes/minecraft/MCX-53300/1603659/