Hopper: java.lang.ClassCastException: vz cannot be cast to axf

This is an automatically generated report based from the following crash: http://hopper.minecraft.net/crashes/minecraft/MCX-10099/

Crash:

java.lang.ClassCastException: vz cannot be cast to axf
	at axd.a(SourceFile:177)
	at awp.b(SourceFile:515)
	at axd.b(SourceFile:411)
	at avv.d(SourceFile:129)
	at axd.d(SourceFile:488)
	at avv.m(SourceFile:109)

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

---- Minecraft Crash Report ----
// Hey, that tickles! Hehehe!

Time: 8/3/13 5:59 PM
Description: Updating screen events

java.lang.ClassCastException: vz cannot be cast to axf
	at axd.a(SourceFile:177)
	at awp.b(SourceFile:515)
	at axd.b(SourceFile:411)
	at avv.d(SourceFile:129)
	at axd.d(SourceFile:488)
	at avv.m(SourceFile:109)
	at atn.k(SourceFile:1157)
	at atn.S(SourceFile:662)
	at atn.d(SourceFile:618)
	at net.minecraft.client.main.Main.main(SourceFile:101)


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

-- Head --
Stacktrace:
	at axd.a(SourceFile:177)
	at awp.b(SourceFile:515)
	at axd.b(SourceFile:411)
	at avv.d(SourceFile:129)
	at axd.d(SourceFile:488)
	at avv.m(SourceFile:109)

-- Affected screen --
Details:
	Screen name: axd

-- Affected level --
Details:
	Level name: MpServer
	All players: 1 total; [bcx['beowell4481'/177, l='MpServer', x=44.30, y=19.62, z=129.41]]
	Chunk stats: MultiplayerChunkCache: 441
	Level seed: 0
	Level generator: ID 00 - default, ver 1. Features enabled: false
	Level generator options: 
	Level spawn location: World: (23,64,241), Chunk: (at 7,4,1 in 1,15; contains blocks 16,0,240 to 31,255,255), Region: (0,0; contains chunks 0,0 to 31,31, blocks 0,0,0 to 511,255,511)
	Level time: 38503 game time, 38503 day time
	Level dimension: 0
	Level storage version: 0x00000 - Unknown?
	Level weather: Rain time: 0 (now: false), thunder time: 0 (now: false)
	Level game mode: Game mode: creative (ID 1). Hardcore: false. Cheats: false
	Forced entities: 21 total; [rl['Bat'/100, l='MpServer', x=108.20, y=30.86, z=159.64], rl['Bat'/98, l='MpServer', x=118.50, y=35.10, z=122.75], rl['Bat'/64, l='MpServer', x=12.08, y=34.71, z=73.54], rl['Bat'/99, l='MpServer', x=119.76, y=42.68, z=116.46], rl['Bat'/65, l='MpServer', x=13.75, y=35.10, z=97.75], rl['Bat'/96, l='MpServer', x=113.38, y=60.10, z=95.53], rl['Bat'/97, l='MpServer', x=125.22, y=41.86, z=108.32], rl['Bat'/76, l='MpServer', x=19.13, y=39.10, z=120.25], rl['Bat'/75, l='MpServer', x=22.09, y=27.05, z=84.69], tw['Villager'/85, l='MpServer', x=57.44, y=64.75, z=131.32], tw['Villager'/84, l='MpServer', x=63.00, y=65.00, z=127.38], bcx['beowell4481'/177, l='MpServer', x=44.30, y=19.62, z=129.41], tw['Villager'/86, l='MpServer', x=61.78, y=65.00, z=127.38], rl['Bat'/59, l='MpServer', x=-10.75, y=43.17, z=70.00], rl['Bat'/93, l='MpServer', x=94.91, y=15.86, z=139.07], rl['Bat'/58, l='MpServer', x=-12.30, y=17.07, z=90.23], rl['Bat'/95, l='MpServer', x=108.56, y=24.43, z=67.85], rw['Sheep'/94, l='MpServer', x=84.50, y=62.00, z=201.50], rw['Sheep'/89, l='MpServer', x=79.50, y=67.00, z=206.50], rl['Bat'/88, l='MpServer', x=72.00, y=13.00, z=127.59], rl['Bat'/60, l='MpServer', x=-23.78, y=13.47, z=90.16]]
	Retry entities: 0 total; []
Stacktrace:
	at bcu.a(SourceFile:284)
	at atn.b(SourceFile:1743)
	at atn.d(SourceFile:627)
	at net.minecraft.client.main.Main.main(SourceFile:101)

-- System Details --
Details:
	Minecraft Version: 1.6.1
	Operating System: Mac OS X (x86_64) version 10.7.5
	Java Version: 1.6.0_45, Apple Inc.
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Apple Inc.
	Memory: 88352408 bytes (84 MB) / 208842752 bytes (199 MB) up to 1065025536 bytes (1015 MB)
	JVM Flags: 1 total; -Xmx1G
	AABB Pool Size: 14262 (798672 bytes; 0 MB) allocated, 2 (112 bytes; 0 MB) used
	Suspicious classes: No suspicious classes found.
	IntCache: cache: 0, tcache: 0, allocated: 3, tallocated: 63
	Launched Version: 1.6.1
	LWJGL: 2.9.0
	OpenGL: Intel HD Graphics 3000 OpenGL Engine GL version 2.1 APPLE-7.32.12, Intel Inc.
	Is Modded: Probably not. Jar signature remains and client brand is untouched.
	Type: Client (map_client.txt)
	Resource Pack: Default
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: 1679 (94024 bytes; 0 MB) allocated, 17 (952 bytes; 0 MB) used

You can see this full report at http://hopper.minecraft.net/crashes/minecraft/MCX-10099/374405/