minecraft crashed

Put the summary of the bug you're having here
the game closed
What I expected to happen was...:
Describe what you thought should happen here

What actually happened was...:

\/
Steps to Reproduce:
1. I made a flatworld out of dirt and grass
2. it closed :/
3. ...

Crash report from the game:

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

Time: 01.07.13 14:47
Description: Unexpected error

java.lang.ArrayIndexOutOfBoundsException: -1
	at acq.a(SourceFile:168)
	at aco.<init>(SourceFile:30)
	at acn.a(SourceFile:59)
	at acn.b(SourceFile:68)
	at acq.a(SourceFile:61)
	at adm.a(SourceFile:865)
	at abr.a(SourceFile:93)
	at acg.a(SourceFile:163)
	at aog.c(SourceFile:73)
	at bfg.p(SourceFile:3620)
	at bfg.b(SourceFile:121)
	at bep.a(SourceFile:160)
	at bfa.a(SourceFile:1122)
	at bet.a(SourceFile:814)
	at bet.b(SourceFile:695)
	at atn.S(SourceFile:685)
	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 acq.a(SourceFile:168)
	at aco.<init>(SourceFile:30)
	at acn.a(SourceFile:59)
	at acn.b(SourceFile:68)
	at acq.a(SourceFile:61)
	at adm.a(SourceFile:865)
	at abr.a(SourceFile:93)
	at acg.a(SourceFile:163)
	at aog.c(SourceFile:73)
	at bfg.p(SourceFile:3620)
	at bfg.b(SourceFile:121)
	at bep.a(SourceFile:160)
	at bfa.a(SourceFile:1122)
	at bet.a(SourceFile:814)

-- Affected level --
Details:
	Level name: MpServer
	All players: 1 total; [bcx['04952'/167, l='MpServer', x=0,50, y=21,73, z=0,50]]
	Chunk stats: MultiplayerChunkCache: 15
	Level seed: 0
	Level generator: ID 00 - default, ver 1. Features enabled: false
	Level generator options: 
	Level spawn location: World: (0,21,0), Chunk: (at 0,1,0 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: 13 game time, 13 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: survival (ID 0). Hardcore: false. Cheats: false
	Forced entities: 1 total; [bcx['04952'/167, l='MpServer', x=0,50, y=21,73, z=0,50]]
	Retry entities: 0 total; []
Stacktrace:
	at bcu.a(SourceFile:284)
	at atn.b(SourceFile:1743)
	at atn.d(SourceFile:632)
	at net.minecraft.client.main.Main.main(SourceFile:101)

-- System Details --
Details:
	Minecraft Version: 1.6.1
	Operating System: Linux (i386) version 3.8.0-25-generic
	Java Version: 1.7.0_21, Oracle Corporation
	Java VM Version: OpenJDK Client VM (mixed mode, sharing), Oracle Corporation
	Memory: 93705488 bytes (89 MB) / 202715136 bytes (193 MB) up to 1037959168 bytes (989 MB)
	JVM Flags: 1 total; -Xmx1G
	AABB Pool Size: 739 (41384 bytes; 0 MB) allocated, 123 (6888 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: Mesa DRI Mobile Intel® GM45 Express Chipset x86/MMX/SSE2 GL version 2.1 Mesa 9.1.3, Intel Open Source Technology Center
	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: 135 (7560 bytes; 0 MB) allocated, 135 (7560 bytes; 0 MB) used