Hopper: java.lang.ArrayIndexOutOfBoundsException: 6

This is an automatically generated report based from the following crash: http://hopper.minecraft.net/crashes/minecraft/MCX-197961/

Crash:

java.lang.ArrayIndexOutOfBoundsException: 6
	at ast.e(SourceFile:382)
	at ast.k(SourceFile:142)
	at ast.a(SourceFile:120)

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

---- Minecraft Crash Report ----
// I just don't know what went wrong :(

Time: 20.09.13 19:38
Description: Exception while updating neighbours

java.lang.ArrayIndexOutOfBoundsException: 6
	at ast.e(SourceFile:382)
	at ast.k(SourceFile:142)
	at ast.a(SourceFile:120)
	at abw.g(SourceFile:469)
	at abw.f(SourceFile:447)
	at ary.k_(SourceFile:278)
	at vj.<init>(SourceFile:14)
	at jv.a(SourceFile:405)
	at ank.a(SourceFile:239)
	at jw.a(SourceFile:247)
	at ka.a(SourceFile:352)
	at gk.a(SourceFile:58)
	at cn.b(SourceFile:64)
	at ka.e(SourceFile:60)
	at kd.b(SourceFile:37)
	at blc.b(SourceFile:84)
	at net.minecraft.server.MinecraftServer.t(SourceFile:489)
	at net.minecraft.server.MinecraftServer.s(SourceFile:406)
	at bkz.s(SourceFile:124)
	at net.minecraft.server.MinecraftServer.run(SourceFile:340)
	at hi.run(SourceFile:583)


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

-- Head --
Stacktrace:
	at ast.e(SourceFile:382)
	at ast.k(SourceFile:142)
	at ast.a(SourceFile:120)

-- Block being updated --
Details:
	Source block type: ID #146 (tile.chestTrap // ank)
	Block type: ID #33 (tile.pistonBase // ast)
	Block data value: 6 / 0x6 / 0b0110
	Block location: World: (-137,74,-681), Chunk: (at 7,4,7 in -9,-43; contains blocks -144,0,-688 to -129,255,-673), Region: (-1,-2; contains chunks -32,-64 to -1,-33, blocks -512,0,-1024 to -1,255,-513)
Stacktrace:
	at abw.g(SourceFile:469)
	at abw.f(SourceFile:447)
	at ary.k_(SourceFile:278)
	at vj.<init>(SourceFile:14)
	at jv.a(SourceFile:405)
	at ank.a(SourceFile:239)
	at jw.a(SourceFile:247)
	at ka.a(SourceFile:352)
	at gk.a(SourceFile:58)
	at cn.b(SourceFile:64)
	at ka.e(SourceFile:60)

-- Ticking connection --
Details:
	Connection: ka@102d6b3
Stacktrace:
	at kd.b(SourceFile:37)
	at blc.b(SourceFile:84)
	at net.minecraft.server.MinecraftServer.t(SourceFile:489)
	at net.minecraft.server.MinecraftServer.s(SourceFile:406)
	at bkz.s(SourceFile:124)
	at net.minecraft.server.MinecraftServer.run(SourceFile:340)
	at hi.run(SourceFile:583)

-- System Details --
Details:
	Minecraft Version: 1.6.4
	Operating System: Windows 7 (x86) version 6.1
	Java Version: 1.7.0_25, Oracle Corporation
	Java VM Version: Java HotSpot(TM) Client VM (mixed mode, sharing), Oracle Corporation
	Memory: 83852312 bytes (79 MB) / 269611008 bytes (257 MB) up to 518979584 bytes (494 MB)
	JVM Flags: 3 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx512M -Xmx512M
	AABB Pool Size: 369 (20664 bytes; 0 MB) allocated, 260 (14560 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: 26 (1456 bytes; 0 MB) allocated, 17 (952 bytes; 0 MB) used
	Player Count: 1 / 8; [jv['Dracothar'/180, l='PMCNetherContest', x=-135,49, y=75,00, z=-680,55]]
	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-197961/12657183/