Hopper: java.lang.IllegalArgumentException: Cannot set property bck{name=facing, clazz=class ei, values=[down, up, north, south, west, east]} to null on block

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)

---- Minecraft Crash Report ----
// This is a token for 1 free hug. Redeem at your nearest Mojangsta: [~~HUG~~]

Time: 09/07/14 16:55
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: Test
	All players: 1 total; [qj['Billy5804'/103, l='Test', x=97.18, y=56.00, z=96.64]]
	Chunk stats: ServerChunkCache: 483 Drop: 0
	Level seed: -7055738240138708059
	Level generator: ID 01 - flat, ver 0. Features enabled: false
	Level generator options: 3;minecraft:bedrock,3*minecraft:stone,52*minecraft:sandstone;2;
	Level spawn location: 88.00,4.00,98.00 - World: (88,4,98), Chunk: (at 8,0,2 in 5,6; contains blocks 80,0,96 to 95,255,111), Region: (0,0; contains chunks 0,0 to 31,31, blocks 0,0,0 to 511,255,511)
	Level time: 67606 game time, 67606 day time
	Level dimension: 0
	Level storage version: 0x04ABD - Anvil
	Level weather: Rain time: 1073 (now: true), thunder time: 6737 (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 7 (amd64) version 6.1
	Java Version: 1.8.0, Oracle Corporation
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
	Memory: 94939584 bytes (90 MB) / 486539264 bytes (464 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: 0, tallocated: 0
	Profiler Position: N/A (disabled)
	Player Count: 1 / 8; [qj['Billy5804'/103, l='Test', x=97.18, y=56.00, z=96.64]]
	Type: Integrated Server (map_client.txt)
	Is Modded: Probably not. Jar signature remains and both client + server brands are untouched.