Random Crashes

Random Crashes on my Survival world

I'm not sure how the crash happens, wether its the new mob ai threading or what but I put the crash report in so I hope this gets adressed:

---- Minecraft Crash Report ----
// Don't be sad. I'll do better next time, I promise!

Time: 7/31/14 12:41 PM
Description: Exception in server tick loop

java.util.ConcurrentModificationException
	at java.util.HashMap$HashIterator.nextEntry(Unknown Source)
	at java.util.HashMap$KeyIterator.next(Unknown Source)
	at qi.a(SourceFile:163)
	at net.minecraft.server.MinecraftServer.y(SourceFile:614)
	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:
---------------------------------------------------------------------------------------

-- System Details --
Details:
	Minecraft Version: 14w31a
	Operating System: Windows 8.1 (amd64) version 6.3
	Java Version: 1.7.0_60, Oracle Corporation
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
	Memory: 304542960 bytes (290 MB) / 929038336 bytes (886 MB) up to 1908932608 bytes (1820 MB)
	JVM Flags: 2 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx2G
	IntCache: cache: 0, tcache: 0, allocated: 13, tallocated: 95
	Profiler Position: N/A (disabled)
	Player Count: 1 / 8; [qr['SquidMan54321'/194, l='Survival 14w31a and up', x=236.03, y=69.10, z=1183.29]]
	Type: Integrated Server (map_client.txt)
	Is Modded: Probably not. Jar signature remains and both client + server brands are untouched.