Breaking dragon's head, activated by redstone signal crashes minecraft.
Step 1 - place dragon's head
Step 2 - activate it with redstone signal
Step 3 - try to break it
Step 4 - game crashes.
Crash report: ---- Minecraft Crash Report ----
// Sorry

Time: 17.08.15 20:36
Description: Rendering entity in world

java.lang.NullPointerException: Rendering entity in world
at acj.j(SourceFile:229)
at bjq.b(SourceFile:50)
at bjq.a(SourceFile:35)
at boa.a(SourceFile:212)
at bny.a(SourceFile:109)
at bny.a(SourceFile:19)
at bnn.a(SourceFile:302)
at bnn.a(SourceFile:267)
at bnn.a(SourceFile:234)
at bjt.a(SourceFile:605)
at bjm.a(SourceFile:1253)
at bjm.b(SourceFile:1158)
at bjm.a(SourceFile:1005)
at ayy.au(SourceFile:905)
at ayy.a(SourceFile:328)
at net.minecraft.client.main.Main.main(SourceFile:125)

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

– Head –
Stacktrace:
at acj.j(SourceFile:229)
at bjq.b(SourceFile:50)
at bjq.a(SourceFile:35)
at boa.a(SourceFile:212)
at bny.a(SourceFile:109)
at bny.a(SourceFile:19)

– Entity being rendered –
Details:
Entity Type: Item (xc)
Entity ID: 13949
Entity Name: ~_ERROR~ NullPointerException: null
Entity's Exact location: -749,44, 70,44, -739,75
Entity's Block location: -750,00,70,00,-740,00 - World: (-750,70,-740), Chunk: (at 2,4,12 in -47,-47; contains blocks -752,0,-752 to -737,255,-737), Region: (-2,-2; contains chunks -64,-64 to -33,-33, blocks -1024,0,-1024 to -513,255,-513)
Entity's Momentum: -0,04, 0,16, -0,08
Entity's Rider: ~_ERROR~ NullPointerException: null
Entity's Vehicle: ~_ERROR~ NullPointerException: null

– Renderer details –
Details:
Assigned renderer: bny@744b4b
Location: -0,66,0,44,0,67 - World: (-1,0,0), Chunk: (at 15,0,0 in -1,0; contains blocks -16,0,0 to -1,255,15), Region: (-1,0; contains chunks -32,0 to -1,31, blocks -512,0,0 to -1,255,511)
Rotation: 67.27658
Delta: 0.54364914
Stacktrace:
at bnn.a(SourceFile:302)
at bnn.a(SourceFile:267)
at bnn.a(SourceFile:234)
at bjt.a(SourceFile:605)
at bjm.a(SourceFile:1253)
at bjm.b(SourceFile:1158)

– Affected level –
Details:
Level name: MpServer
All players: 1 total; [biz['FarmArt'/180, l='MpServer', x=-748,78, y=70,00, z=-740,42]]
Chunk stats: MultiplayerChunkCache: 214, 214
Level seed: 0
Level generator: ID 00 - default, ver 1. Features enabled: false
Level generator options:
Level spawn location: -439,00,64,00,-756,00 - World: (-439,64,-756), Chunk: (at 9,4,12 in -28,-48; contains blocks -448,0,-768 to -433,255,-753), Region: (-1,-2; contains chunks -32,-64 to -1,-33, blocks -512,0,-1024 to -1,255,-513)
Level time: 19185 game time, 26788 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: ~_ERROR~ NullPointerException: null
Retry entities: 0 total; []
Server brand: vanilla
Server type: Integrated singleplayer server
Stacktrace:
at bhb.a(SourceFile:314)
at ayy.b(SourceFile:2297)
at ayy.a(SourceFile:337)
at net.minecraft.client.main.Main.main(SourceFile:125)

– System Details –
Details:
Minecraft Version: 15w33c
Operating System: Windows 7 (x86) version 6.1
Java Version: 1.8.0_45, Oracle Corporation
Java VM Version: Java HotSpot(TM) Client VM (mixed mode), Oracle Corporation
Memory: 122795480 bytes (117 MB) / 405741568 bytes (386 MB) up to 523501568 bytes (499 MB)
JVM Flags: 6 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx512M -XX:+UseConcMarkSweepGC -XX:+CMSIncrementalMode -XX:-UseAdaptiveSizePolicy -Xmn128M
IntCache: cache: 0, tcache: 0, allocated: 13, tallocated: 95
Launched Version: 15w33c
LWJGL: 2.9.4
OpenGL: ATI Mobility Radeon HD 5470 GL version 3.2.9704 Compatibility Profile Context, 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.
VBOs are available because OpenGL 1.5 is supported.

Using VBOs: No
Is Modded: Probably not. Jar signature remains and client brand is untouched.
Type: Client (map_client.txt)
Resource Packs: FarmArt resource pack V3.3.zip (incompatible)
Current Language: Русский (Россия)
Profiler Position: N/A (disabled)
CPU: 4x Intel(R) Core(TM) i3 CPU M 370 @ 2.40GHz