Hopper: java.util.ConcurrentModificationException

java.util.ConcurrentModificationException
	at java.util.HashMap$HashIterator.nextEntry(Unknown Source)
	at java.util.HashMap$KeyIterator.next(Unknown Source)
	at java.util.AbstractCollection.toArray(Unknown Source)
	at java.util.ArrayList.<init>(Unknown Source)
	at alm.e(SourceFile:64)
	at alm.a(SourceFile:208)

---- Minecraft Crash Report ----
// Would you like a cupcake?

Time: 26/10/13 17:21
Description: Exception while updating neighbours

java.util.ConcurrentModificationException
	at java.util.HashMap$HashIterator.nextEntry(Unknown Source)
	at java.util.HashMap$KeyIterator.next(Unknown Source)
	at java.util.AbstractCollection.toArray(Unknown Source)
	at java.util.ArrayList.<init>(Unknown Source)
	at alm.e(SourceFile:64)
	at alm.a(SourceFile:208)
	at afn.e(SourceFile:480)
	at afn.d(SourceFile:462)
	at alm.e(SourceFile:68)
	at alm.a(SourceFile:208)
	at afn.e(SourceFile:480)
	at afn.d(SourceFile:458)
	at alm.e(SourceFile:68)
	at alm.a(SourceFile:208)
	at afn.e(SourceFile:480)
	at afn.d(SourceFile:458)
	at alm.e(SourceFile:68)
	at alm.a(SourceFile:208)
	at afn.e(SourceFile:480)
	at afn.d(SourceFile:458)
	at alm.e(SourceFile:68)
	at alm.a(SourceFile:208)
	at afn.e(SourceFile:480)
	at afn.d(SourceFile:458)
	at alm.e(SourceFile:68)
	at alm.a(SourceFile:208)
	at afn.e(SourceFile:480)
	at aiv.e(SourceFile:238)
	at alr.a(SourceFile:132)
	at aoj.a(SourceFile:428)
	at afn.d(SourceFile:327)
	at aiv.a(SourceFile:52)
	at mj.a(SourceFile:405)
	at mj.b(SourceFile:134)
	at net.minecraft.server.MinecraftServer.u(SourceFile:503)
	at net.minecraft.server.MinecraftServer.t(SourceFile:441)
	at bsk.t(SourceFile:117)
	at net.minecraft.server.MinecraftServer.run(SourceFile:358)
	at ky.run(SourceFile:617)


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

-- Head --
Stacktrace:
	at java.util.HashMap$HashIterator.nextEntry(Unknown Source)
	at java.util.HashMap$KeyIterator.next(Unknown Source)
	at java.util.AbstractCollection.toArray(Unknown Source)
	at java.util.ArrayList.<init>(Unknown Source)
	at alm.e(SourceFile:64)
	at alm.a(SourceFile:208)

-- Block being updated --
Details:
	Source block type: ID #55 (tile.redstoneDust // alm)
	Block type: ID #55 (tile.redstoneDust // alm)
	Block data value: 0 / 0x0 / 0b0000
	Block location: World: (-141,189,-92), Chunk: (at 3,11,4 in -9,-6; contains blocks -144,0,-96 to -129,255,-81), Region: (-1,-1; contains chunks -32,-32 to -1,-1, blocks -512,0,-512 to -1,255,-1)
Stacktrace:
	at afn.e(SourceFile:480)
	at afn.d(SourceFile:462)
	at alm.e(SourceFile:68)
	at alm.a(SourceFile:208)

-- Block being updated --
Details:
	Source block type: ID #55 (tile.redstoneDust // alm)
	Block type: ID #55 (tile.redstoneDust // alm)
	Block data value: 0 / 0x0 / 0b0000
	Block location: World: (-141,189,-90), Chunk: (at 3,11,6 in -9,-6; contains blocks -144,0,-96 to -129,255,-81), Region: (-1,-1; contains chunks -32,-32 to -1,-1, blocks -512,0,-512 to -1,255,-1)
Stacktrace:
	at afn.e(SourceFile:480)
	at afn.d(SourceFile:458)
	at alm.e(SourceFile:68)
	at alm.a(SourceFile:208)

-- Block being updated --
Details:
	Source block type: ID #55 (tile.redstoneDust // alm)
	Block type: ID #55 (tile.redstoneDust // alm)
	Block data value: 0 / 0x0 / 0b0000
	Block location: World: (-141,189,-90), Chunk: (at 3,11,6 in -9,-6; contains blocks -144,0,-96 to -129,255,-81), Region: (-1,-1; contains chunks -32,-32 to -1,-1, blocks -512,0,-512 to -1,255,-1)
Stacktrace:
	at afn.e(SourceFile:480)
	at afn.d(SourceFile:458)
	at alm.e(SourceFile:68)
	at alm.a(SourceFile:208)

-- Block being updated --
Details:
	Source block type: ID #55 (tile.redstoneDust // alm)
	Block type: ID #55 (tile.redstoneDust // alm)
	Block data value: 0 / 0x0 / 0b0000
	Block location: World: (-141,189,-90), Chunk: (at 3,11,6 in -9,-6; contains blocks -144,0,-96 to -129,255,-81), Region: (-1,-1; contains chunks -32,-32 to -1,-1, blocks -512,0,-512 to -1,255,-1)
Stacktrace:
	at afn.e(SourceFile:480)
	at afn.d(SourceFile:458)
	at alm.e(SourceFile:68)
	at alm.a(SourceFile:208)

-- Block being updated --
Details:
	Source block type: ID #55 (tile.redstoneDust // alm)
	Block type: ID #55 (tile.redstoneDust // alm)
	Block data value: 0 / 0x0 / 0b0000
	Block location: World: (-141,189,-90), Chunk: (at 3,11,6 in -9,-6; contains blocks -144,0,-96 to -129,255,-81), Region: (-1,-1; contains chunks -32,-32 to -1,-1, blocks -512,0,-512 to -1,255,-1)
Stacktrace:
	at afn.e(SourceFile:480)
	at afn.d(SourceFile:458)
	at alm.e(SourceFile:68)
	at alm.a(SourceFile:208)

-- Block being updated --
Details:
	Source block type: ID #94 (tile.diode // alr)
	Block type: ID #55 (tile.redstoneDust // alm)
	Block data value: 0 / 0x0 / 0b0000
	Block location: World: (-141,189,-90), Chunk: (at 3,11,6 in -9,-6; contains blocks -144,0,-96 to -129,255,-81), Region: (-1,-1; contains chunks -32,-32 to -1,-1, blocks -512,0,-512 to -1,255,-1)
Stacktrace:
	at afn.e(SourceFile:480)
	at aiv.e(SourceFile:238)
	at alr.a(SourceFile:132)
	at aoj.a(SourceFile:428)
	at afn.d(SourceFile:327)
	at aiv.a(SourceFile:52)

-- Block being ticked --
Details:
	Block type: ID #94 (tile.diode // alr)
	Block data value: 2 / 0x2 / 0b0010
	Block location: World: (-141,189,-91), Chunk: (at 3,11,5 in -9,-6; contains blocks -144,0,-96 to -129,255,-81), Region: (-1,-1; contains chunks -32,-32 to -1,-1, blocks -512,0,-512 to -1,255,-1)
Stacktrace:
	at mj.a(SourceFile:405)
	at mj.b(SourceFile:134)

-- Affected level --
Details:
	Level name: Search for the Skyheart
	All players: 0 total; []
	Chunk stats: ServerChunkCache: 662 Drop: 309
	Level seed: 141107
	Level generator: ID 01 - flat, ver 0. Features enabled: false
	Level generator options: 
	Level spawn location: World: (113,141,59), Chunk: (at 1,8,11 in 7,3; contains blocks 112,0,48 to 127,255,63), Region: (0,0; contains chunks 0,0 to 31,31, blocks 0,0,0 to 511,255,511)
	Level time: 7925583 game time, 11054 day time
	Level dimension: 0
	Level storage version: 0x04ABD - Anvil
	Level weather: Rain time: 167983 (now: false), thunder time: 44833 (now: false)
	Level game mode: Game mode: adventure (ID 2). Hardcore: false. Cheats: true
Stacktrace:
	at net.minecraft.server.MinecraftServer.u(SourceFile:503)
	at net.minecraft.server.MinecraftServer.t(SourceFile:441)
	at bsk.t(SourceFile:117)
	at net.minecraft.server.MinecraftServer.run(SourceFile:358)
	at ky.run(SourceFile:617)

-- System Details --
Details:
	Minecraft Version: 1.7.2
	Operating System: Windows 7 (amd64) version 6.1
	Java Version: 1.7.0_25, Oracle Corporation
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
	Memory: 92203240 bytes (87 MB) / 295239680 bytes (281 MB) up to 954466304 bytes (910 MB)
	JVM Flags: 2 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx1G
	AABB Pool Size: 250 (14000 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
	IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: 17 (952 bytes; 0 MB) allocated, 0 (0 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.