Baby Zombies Spawner crash the game

I created "Baby Zombies" spawner with MCEdit.

In other versions, such as 13w19 or 13w18, everything works fine, but in 13w21, 13w22 and 13w23 the game crash.

This also occurs with Baby Zombies pigmen.

I suppose it's something unintentional, so I reported.

I have attached the crash report.

_{Sorry for my bad English, is not my native language.}

Crash report:

---- Minecraft Crash Report ----
// Everything's going to plan. No, really, that was supposed to happen.

Time: 12/06/13 22:24
Description: Loading entity NBT

java.lang.UnsupportedOperationException: Cannot modify readonly attribute
	at om.b(SourceFile:59)
	at ti.a(SourceFile:107)
	at ti.a(SourceFile:290)
	at na.f(SourceFile:1061)
	at aax.a(SourceFile:116)
	at aax.h(SourceFile:234)
	at bht.a(SourceFile:22)
	at bht.a(SourceFile:17)
	at bht.a(SourceFile:12)
	at bhy.a(SourceFile:106)
	at bhy.a(SourceFile:98)
	at bei.a(SourceFile:317)
	at beb.a(SourceFile:834)
	at beb.b(SourceFile:682)
	at atc.R(SourceFile:683)
	at atc.d(SourceFile:616)
	at net.minecraft.client.main.Main.main(SourceFile:82)


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

-- Head --
Stacktrace:
	at om.b(SourceFile:59)
	at ti.a(SourceFile:107)
	at ti.a(SourceFile:290)

-- Entity being loaded --
Details:
	Entity Type: Zombie (ti)
	Entity ID: 116
	Entity Name: Zombi
	Entity's Exact location: 0,00, 0,00, 0,00
	Entity's Block location: World: (0,0,0), Chunk: (at 0,0,0 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)
	Entity's Momentum: 0,00, 0,00, 0,00
Stacktrace:
	at na.f(SourceFile:1061)
	at aax.a(SourceFile:116)
	at aax.h(SourceFile:234)
	at bht.a(SourceFile:22)
	at bht.a(SourceFile:17)
	at bht.a(SourceFile:12)

-- Tile Entity Details --
Details:
	Name: MobSpawner // arr
	Block type: ID #52 (tile.mobSpawner // aoq)
	Block data value: 0 / 0x0 / 0b0000
	Block location: World: (-230,4,651), Chunk: (at 10,0,11 in -15,40; contains blocks -240,0,640 to -225,255,655), Region: (-1,1; contains chunks -32,32 to -1,63, blocks -512,0,512 to -1,255,1023)
	Actual block type: ID #52 (tile.mobSpawner // aoq)
	Actual block data value: 0 / 0x0 / 0b0000
Stacktrace:
	at bhy.a(SourceFile:106)
	at bhy.a(SourceFile:98)
	at bei.a(SourceFile:317)
	at beb.a(SourceFile:834)

-- Affected level --
Details:
	Level name: MpServer
	All players: 1 total; [bcf['Lord_Kaydan'/11, l='MpServer', x=-225,71, y=5,62, z=642,90]]
	Chunk stats: MultiplayerChunkCache: 110
	Level seed: 0
	Level generator: ID 01 - flat, ver 0. Features enabled: false
	Level generator options: 
	Level spawn location: World: (-309,4,644), Chunk: (at 11,0,4 in -20,40; contains blocks -320,0,640 to -305,255,655), Region: (-1,1; contains chunks -32,32 to -1,63, blocks -512,0,512 to -1,255,1023)
	Level time: 35305 game time, 67049 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: 11 total; [ti['Zombi'/1, l='MpServer', x=-241,34, y=3,00, z=664,26], ti['Zombi'/2, l='MpServer', x=-236,50, y=3,00, z=639,16], ti['Zombi'/3, l='MpServer', x=-236,44, y=4,00, z=653,59], ti['Zombi'/4, l='MpServer', x=-239,16, y=4,00, z=642,97], ti['Zombi'/5, l='MpServer', x=-229,56, y=4,00, z=649,50], ti['Zombi'/6, l='MpServer', x=-229,63, y=4,00, z=650,44], ti['Zombi'/7, l='MpServer', x=-237,03, y=4,00, z=646,47], ti['Zombi'/8, l='MpServer', x=-226,84, y=4,00, z=644,38], ti['Zombi'/9, l='MpServer', x=-237,53, y=5,00, z=652,66], ti['Zombi'/10, l='MpServer', x=-238,13, y=4,00, z=650,31], bcf['Lord_Kaydan'/11, l='MpServer', x=-225,71, y=5,62, z=642,90]]
	Retry entities: 0 total; []
Stacktrace:
	at bcc.a(SourceFile:282)
	at atc.b(SourceFile:1795)
	at atc.d(SourceFile:625)
	at net.minecraft.client.main.Main.main(SourceFile:82)

-- System Details --
Details:
	Minecraft Version: 13w23b
	Operating System: Windows 7 (amd64) version 6.1
	Java Version: 1.7.0_07, Oracle Corporation
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
	Memory: 103724960 bytes (98 MB) / 359727104 bytes (343 MB) up to 954466304 bytes (910 MB)
	JVM Flags: 1 total; -Xmx1G
	AABB Pool Size: 21639 (1211784 bytes; 1 MB) allocated, 2115 (118440 bytes; 0 MB) used
	Suspicious classes: No suspicious classes found.
	IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
	Launched Version: 13w23b
	LWJGL: 2.9.0
	OpenGL: AMD Radeon HD 6750M GL version 4.1.10428 Compatibility Profile Context, ATI Technologies Inc.
	Is Modded: Probably not. Jar signature remains and client brand is untouched.
	Type: Client (map_client.txt)
	Texture Pack: Default
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: 508 (28448 bytes; 0 MB) allocated, 272 (15232 bytes; 0 MB) used