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
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This is what you get, Mojang, for removing piston_extension!
it isn't removed, the one placed is not a supported data value

Is this still a concern in the current Minecraft version? If so, please update the affected versions in order to best aid Mojang ensuring bugs are still valid in the latest releases/pre-releases. If this has been done, we can reopen the issue.
Keep in mind that the "Resolved"-Status on this ticket just means "Answered", and that we are waiting for further information on whether this issue still exists or not. We will reopen it as soon as the requested information has been delivered.
Ticket resolved as incomplete, because no answer in a reasonable amount of time (1+ year), if it still happens, please update the ticket.