minecraft:piston_head: Cannot set property

I make a digital clock with redstone, but sometimes minecraft crashes and this is the crash report:

---- Minecraft Crash Report ----
// You should try our sister game, Minceraft!

Time: 3/07/14 05:17 PM
Description: Rendering Block Entity

java.lang.IllegalArgumentException: Cannot set property azi{name=facing, clazz=class dw, values=[down, up, north, south, west, east]} to null on block minecraft:piston_head, it is not an allowed value
	at ayx.a(SourceFile:132)
	at aym.b(SourceFile:203)
	at che.a(SourceFile:31)
	at che.a(SourceFile:24)
	at cgy.a(SourceFile:104)
	at cgy.a(SourceFile:96)
	at ceh.a(SourceFile:513)
	at cdn.a(SourceFile:1194)
	at cdn.a(SourceFile:1121)
	at cdn.b(SourceFile:973)
	at bmi.ap(SourceFile:886)
	at bmi.a(SourceFile:303)
	at net.minecraft.client.main.Main.main(SourceFile:120)


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

-- Head --
Stacktrace:
	at ayx.a(SourceFile:132)
	at aym.b(SourceFile:203)
	at che.a(SourceFile:31)
	at che.a(SourceFile:24)

-- Block Entity Details --
Details:
	Name: Piston // ayq
	Block type: ID #35 (tile.cloth // apv)
	Block data value: 1 / 0x1 / 0b0001
	Block location: World: (-31,64,113), Chunk: (at 1,4,1 in -2,7; contains blocks -32,0,112 to -17,255,127), Region: (-1,0; contains chunks -32,0 to -1,31, blocks -512,0,0 to -1,255,511)
	Actual block type: ID #35 (tile.cloth // apv)
	Actual block data value: 7 / 0x7 / 0b0111
Stacktrace:
	at cgy.a(SourceFile:104)
	at cgy.a(SourceFile:96)
	at ceh.a(SourceFile:513)
	at cdn.a(SourceFile:1194)
	at cdn.a(SourceFile:1121)

-- Affected level --
Details:
	Level name: MpServer
	All players: 1 total; [ccx['Capi2000'/56, l='MpServer', x=-16.94, y=63.00, z=76.24]]
	Chunk stats: MultiplayerChunkCache: 284, 284
	Level seed: 0
	Level generator: ID 00 - default, ver 1. Features enabled: false
	Level generator options: 
	Level spawn location: 0.00,64.00,0.00 - World: (0,64,0), 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: 974876 game time, 6000 day time
	Level dimension: 0
	Level storage version: 0x00000 - Unknown?
	Level weather: Rain time: 0 (now: false), thunder time: 0 (now: false)
	Level game mode: Game mode: creative (ID 1). Hardcore: false. Cheats: false
	Forced entities: 22 total; [ccx['Capi2000'/56, l='MpServer', x=-16.94, y=63.00, z=76.24], yz['Murciélago'/11, l='MpServer', x=-73.06, y=22.10, z=17.22], yz['Murciélago'/15, l='MpServer', x=-27.53, y=55.10, z=48.88], aaz['entity.MinecartRideable.name'/16, l='MpServer', x=-40.88, y=64.93, z=112.93], yz['Murciélago'/19, l='MpServer', x=-26.78, y=54.10, z=47.75], zw['Calamar'/21, l='MpServer', x=-2.06, y=60.98, z=83.94], yz['Murciélago'/20, l='MpServer', x=-31.31, y=56.10, z=54.28], yz['Murciélago'/23, l='MpServer', x=-7.28, y=18.10, z=-0.59], zw['Calamar'/22, l='MpServer', x=-16.77, y=55.90, z=83.38], zw['Calamar'/24, l='MpServer', x=5.30, y=59.78, z=73.43], zd['Caballo'/27, l='MpServer', x=20.00, y=63.00, z=78.25], zw['Calamar'/28, l='MpServer', x=26.81, y=58.91, z=97.06], zw['Calamar'/31, l='MpServer', x=23.91, y=58.38, z=104.22], zw['Calamar'/30, l='MpServer', x=22.78, y=58.38, z=97.16], yz['Murciélago'/22744, l='MpServer', x=-2.34, y=52.89, z=43.56], yz['Murciélago'/436315, l='MpServer', x=11.53, y=43.02, z=13.28], zw['Calamar'/33, l='MpServer', x=15.72, y=61.03, z=103.66], yz['Murciélago'/38, l='MpServer', x=30.53, y=23.97, z=128.66], zw['Calamar'/36, l='MpServer', x=23.03, y=60.13, z=128.53], yz['Murciélago'/22669, l='MpServer', x=-4.31, y=42.06, z=134.81], yz['Murciélago'/22671, l='MpServer', x=-18.44, y=38.78, z=151.25], vf['entity.LeashKnot.name'/55, l='MpServer', x=21.50, y=63.50, z=78.50]]
	Retry entities: 0 total; []
	Server brand: vanilla
	Server type: Integrated singleplayer server
Stacktrace:
	at bza.a(SourceFile:310)
	at bmi.b(SourceFile:2135)
	at bmi.a(SourceFile:312)
	at net.minecraft.client.main.Main.main(SourceFile:120)

-- System Details --
Details:
	Minecraft Version: 14w27b
	Operating System: Windows 8 (amd64) version 6.2
	Java Version: 1.7.0_45, Oracle Corporation
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
	Memory: 161408752 bytes (153 MB) / 494927872 bytes (472 MB) up to 831520768 bytes (793 MB)
	JVM Flags: 1 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump
	IntCache: cache: 0, tcache: 0, allocated: 12, tallocated: 94
	Launched Version: 14w27b
	LWJGL: 2.9.1
	OpenGL: AMD Radeon(TM) HD 6480G GL version 4.3.12618 Compatibility Profile Context 13.251.0.0, ATI Technologies Inc.
	GL Caps: Using GL 1.3 multitexturing.
Using GL 1.3 texture combiners.
Using framebuffer objects because OpenGL 3.0 is supported and separate blending is supported.
Shaders are available because OpenGL 2.1 is supported.

	Is Modded: Probably not. Jar signature remains and client brand is untouched.
	Type: Client (map_client.txt)
	Resource Packs: []
	Current Language: Español (México)
	Profiler Position: N/A (disabled)

This isn't about the crash report: I can't play with this crash, because sometimes, when my clock changes a number, minecraft crashes. Please, correct that error. I send you my world to check it, because maybe the problem is my world, i don't know, but I think that Minecraft is the problem. I need urgently the release of the 1.8 version