---- Minecraft Crash Report ----
// But it works on my machine.

Time: 10.07.14 13:35
Description: Exception ticking world

java.lang.IllegalArgumentException: Cannot set property bck

{name=facing, clazz=class ei, values=[down, up, north, south, west, east]}

to null on block minecraft:piston_extension, it is not an allowed value
at bbw.a(SourceFile:103)
at bbn.b(SourceFile:208)
at bbi.a(SourceFile:365)
at bbi.a(SourceFile:152)
at qg.a(SourceFile:853)
at qg.aj(SourceFile:842)
at qg.c(SourceFile:214)
at net.minecraft.server.MinecraftServer.x(SourceFile:578)
at net.minecraft.server.MinecraftServer.w(SourceFile:510)
at cwg.w(SourceFile:132)
at net.minecraft.server.MinecraftServer.run(SourceFile:426)
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 bbw.a(SourceFile:103)
at bbn.b(SourceFile:208)
at bbi.a(SourceFile:365)
at bbi.a(SourceFile:152)
at qg.a(SourceFile:853)
at qg.aj(SourceFile:842)
at qg.c(SourceFile:214)

– Affected level –
Details:
Level name: New World
All players: 1 total; [qj['Knuspermann'/241, l='New World', x=-47,70, y=68,00, z=188,30]]
Chunk stats: ServerChunkCache: 699 Drop: 0
Level seed: 7702919137565700418
Level generator: ID 00 - default, ver 1. Features enabled: true
Level generator options:
Level spawn location: -52,00,64,00,193,00 - World: (-52,64,193), Chunk: (at 12,4,1 in -4,12; contains blocks -64,0,192 to -49,255,207), Region: (-1,0; contains chunks -32,0 to -1,31, blocks -512,0,0 to -1,255,511)
Level time: 2150 game time, 2150 day time
Level dimension: 0
Level storage version: 0x04ABD - Anvil
Level weather: Rain time: 137431 (now: false), thunder time: 68847 (now: false)
Level game mode: Game mode: creative (ID 1). Hardcore: false. Cheats: true
Stacktrace:
at net.minecraft.server.MinecraftServer.x(SourceFile:578)
at net.minecraft.server.MinecraftServer.w(SourceFile:510)
at cwg.w(SourceFile:132)
at net.minecraft.server.MinecraftServer.run(SourceFile:426)
at java.lang.Thread.run(Unknown Source)

– System Details –
Details:
Minecraft Version: 14w28a
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: 283618504 bytes (270 MB) / 630718464 bytes (601 MB) up to 954728448 bytes (910 MB)
JVM Flags: 2 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx1G
IntCache: cache: 0, tcache: 0, allocated: 13, tallocated: 95
Profiler Position: N/A (disabled)
Player Count: 1 / 8; [qj['Knuspermann'/241, l='New World', x=-47,70, y=68,00, z=188,30]]
Type: Integrated Server (map_client.txt)
Is Modded: Probably not. Jar signature remains and both client + server brands are untouched.