Random crash "Exception ticking world"

---- Minecraft Crash Report ----
// Surprise! Haha. Well, this is awkward.

Time: 30.07.14 22:03
Description: Exception ticking world

java.util.ConcurrentModificationException
	at java.util.AbstractList$Itr.checkForComodification(Unknown Source)
	at java.util.AbstractList$Itr.next(Unknown Source)
	at aqh.a(SourceFile:2316)
	at aqt.a(SourceFile:73)
	at qo.c(SourceFile:182)
	at net.minecraft.server.MinecraftServer.y(SourceFile:598)
	at net.minecraft.server.MinecraftServer.x(SourceFile:530)
	at cxc.x(SourceFile:155)
	at net.minecraft.server.MinecraftServer.run(SourceFile:446)
	at java.lang.Thread.run(Unknown Source)


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

-- Head --
Stacktrace:
	at java.util.AbstractList$Itr.checkForComodification(Unknown Source)
	at java.util.AbstractList$Itr.next(Unknown Source)
	at aqh.a(SourceFile:2316)
	at aqt.a(SourceFile:73)
	at qo.c(SourceFile:182)

-- Affected level --
Details:
	Level name: Testworld
	All players: 1 total; [qr['Marcono1234'/30611261, l='Testworld', x=-394,75, y=7,86, z=1125,43]]
	Chunk stats: ServerChunkCache: 471 Drop: 0
	Level seed: 5107690527965591543
	Level generator: ID 01 - flat, ver 0. Features enabled: true
	Level generator options: 3;;2;
	Level spawn location: -348,00,4,00,1139,00 - World: (-348,4,1139), Chunk: (at 4,0,3 in -22,71; contains blocks -352,0,1136 to -337,255,1151), Region: (-1,2; contains chunks -32,64 to -1,95, blocks -512,0,1024 to -1,255,1535)
	Level time: 56524 game time, 64393 day time
	Level dimension: 0
	Level storage version: 0x04ABD - Anvil
	Level weather: Rain time: 33116 (now: false), thunder time: 63691 (now: false)
	Level game mode: Game mode: creative (ID 1). Hardcore: false. Cheats: true
Stacktrace:
	at net.minecraft.server.MinecraftServer.y(SourceFile:598)
	at net.minecraft.server.MinecraftServer.x(SourceFile:530)
	at cxc.x(SourceFile:155)
	at net.minecraft.server.MinecraftServer.run(SourceFile:446)
	at java.lang.Thread.run(Unknown Source)

-- System Details --
Details:
	Minecraft Version: 14w31a
	Operating System: Windows 7 (amd64) version 6.1
	Java Version: 1.6.0_45, Sun Microsystems Inc.
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Sun Microsystems Inc.
	Memory: 123199928 bytes (117 MB) / 329904128 bytes (314 MB) up to 1060372480 bytes (1011 MB)
	JVM Flags: 6 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx1G -XX:+UseConcMarkSweepGC -XX:+CMSIncrementalMode -XX:-UseAdaptiveSizePolicy -Xmn128M
	IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
	Profiler Position: N/A (disabled)
	Player Count: 1 / 8; [qr['Marcono1234'/30611261, l='Testworld', x=-394,75, y=7,86, z=1125,43]]
	Type: Integrated Server (map_client.txt)
	Is Modded: Probably not. Jar signature remains and both client + server brands are untouched.
#@!@# Game crashed! Crash report saved to: #@!@# C:\Users\Markus\AppData\Roaming\.minecraft\crash-reports\crash-2014-07-30_22.03.21-server.txt
[22:03:21] [Client Shutdown Thread/INFO]: Stopping server
[22:03:21] [Server thread/INFO]: Marcono1234 lost connection: TextComponent{text='Server closed', siblings=[], style=Style{hasParent=false, color=null, bold=null, italic=null, underlined=null, obfuscated=null, clickEvent=null, hoverEvent=null, insertion=null}}
[22:03:21] [Server thread/INFO]: Marcono1234 hat das Spiel verlassen