Problem Executing Command Block

When i loaded my world, it loaded up fine but when the chunk with the command blocks loaded, the game crashed and it said:"Problem Executing Command Block". This issue has only happened once to me, so this bug is rare, but it was annoying because i was busy doing stuff in that world.
Steps to reproduce
You may have to do this several hundred or thousand times for it to happen!
1. Create new world
2. Obtain Command Blocks
3. Type in this command:tp @e[type=Enderman] ~ -200 ~ or somthing else
4. Save and quit the world
5. Load the world again
6. Sometimes when you load the world again but it's rare, the game will crash saying:

---- Minecraft Crash Report ----
// Sorry :(

Time: 6/2/14 3:49 PM
Description: Executing command block

java.lang.NullPointerException: Executing command block
	at java.util.Collections.addAll(Unknown Source)
	at ad.b(SourceFile:152)
	at z.a(SourceFile:47)
	at akw.a(SourceFile:92)
	at aos.b(SourceFile:60)
	at oq.a(SourceFile:482)
	at oq.c(SourceFile:193)
	at net.minecraft.server.MinecraftServer.w(SourceFile:570)
	at net.minecraft.server.MinecraftServer.v(SourceFile:506)
	at cln.v(SourceFile:132)
	at net.minecraft.server.MinecraftServer.run(SourceFile:422)
	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.Collections.addAll(Unknown Source)
	at ad.b(SourceFile:152)
	at z.a(SourceFile:47)

-- Command to be executed --
Details:
	Command: tp @e[type=Enderman] ~ -200 ~
	Name: @
Stacktrace:
	at akw.a(SourceFile:92)
	at aos.b(SourceFile:60)

-- Block being ticked --
Details:
	Block type: ID #137 (tile.commandBlock // aos)
	Block data value: 1 / 0x1 / 0b0001
	Block location: World: (21,68,-41), Chunk: (at 5,4,7 in 1,-3; contains blocks 16,0,-48 to 31,255,-33), Region: (0,-1; contains chunks 0,-32 to 31,-1, blocks 0,0,-512 to 511,255,-1)
Stacktrace:
	at oq.a(SourceFile:482)
	at oq.c(SourceFile:193)

-- Affected level --
Details:
	Level name: DonGlitchy's Survival World
	All players: 0 total; []
	Chunk stats: ServerChunkCache: 527 Drop: 81
	Level seed: 27594263
	Level generator: ID 02 - largeBiomes, ver 0. Features enabled: true
	Level generator options: 
	Level spawn location: 0.00,69.00,0.00 - World: (0,69,0), Chunk: (at 0,4,0 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: 280077 game time, 5802 day time
	Level dimension: 0
	Level storage version: 0x04ABD - Anvil
	Level weather: Rain time: 1 (now: false), thunder time: 1 (now: false)
	Level game mode: Game mode: creative (ID 1). Hardcore: false. Cheats: true
Stacktrace:
	at net.minecraft.server.MinecraftServer.w(SourceFile:570)
	at net.minecraft.server.MinecraftServer.v(SourceFile:506)
	at cln.v(SourceFile:132)
	at net.minecraft.server.MinecraftServer.run(SourceFile:422)
	at java.lang.Thread.run(Unknown Source)

-- System Details --
Details:
	Minecraft Version: 14w21b
	Operating System: Windows 7 (x86) version 6.1
	Java Version: 1.7.0_55, Oracle Corporation
	Java VM Version: Java HotSpot(TM) Client VM (mixed mode), Oracle Corporation
	Memory: 138866016 bytes (132 MB) / 226037760 bytes (215 MB) up to 944701440 bytes (900 MB)
	JVM Flags: 3 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx512M -Xmx932M
	IntCache: cache: 0, tcache: 0, allocated: 13, tallocated: 99
	Profiler Position: N/A (disabled)
	Player Count: 0 / 8; []
	Type: Integrated Server (map_client.txt)
	Is Modded: Probably not. Jar signature remains and both client + server brands are untouched.