When I tried to be over 254 I get a crash, the following crash:
---- Minecraft Crash Report ----
// Quite honestly, I wouldn't worry myself about that.
Time: 18/08/14 16:27
Description: Unexpected error
java.lang.NullPointerException: Unexpected error
at cki.a(SourceFile:798)
at cjd.a(SourceFile:1189)
at cjd.a(SourceFile:1123)
at cjd.b(SourceFile:976)
at bsr.as(SourceFile:901)
at bsr.a(SourceFile:312)
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 cki.a(SourceFile:798)
at cjd.a(SourceFile:1189)
at cjd.a(SourceFile:1123)
-- Affected level --
Details:
Level name: MpServer
All players: 1 total; [cij['lAngelP'/503, l='MpServer', x=-186,74, y=254,69, z=-171,76]]
Chunk stats: MultiplayerChunkCache: 450, 450
Level seed: 0
Level generator: ID 00 - default, ver 1. Features enabled: false
Level generator options:
Level spawn location: -179,00,64,00,-166,00 - World: (-179,64,-166), Chunk: (at 13,4,10 in -12,-11; contains blocks -192,0,-176 to -177,255,-161), Region: (-1,-1; contains chunks -32,-32 to -1,-1, blocks -512,0,-512 to -1,255,-1)
Level time: 665 game time, 665 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: 78 total; [acn['Squid'/75982, l='MpServer', x=-173,50, y=51,00, z=-111,50], acn['Squid'/75983, l='MpServer', x=-175,50, y=51,00, z=-108,50], acn['Squid'/75980, l='MpServer', x=-170,50, y=62,00, z=-198,50], agb['Spider'/74776, l='MpServer', x=-129,50, y=14,00, z=-212,50], acn['Squid'/75981, l='MpServer', x=-174,50, y=51,00, z=-113,50], acn['Squid'/77473, l='MpServer', x=-126,50, y=47,00, z=-109,50], acn['Squid'/75979, l='MpServer', x=-169,50, y=62,00, z=-201,50], acn['Squid'/75977, l='MpServer', x=-165,50, y=62,00, z=-201,50], acn['Squid'/75972, l='MpServer', x=-164,50, y=62,00, z=-202,50], acn['Squid'/75988, l='MpServer', x=-148,50, y=54,00, z=-201,50], acn['Squid'/75987, l='MpServer', x=-150,50, y=54,00, z=-199,50], acn['Squid'/75986, l='MpServer', x=-149,50, y=54,00, z=-201,50], acn['Squid'/75985, l='MpServer', x=-149,50, y=54,00, z=-198,50], acn['Squid'/75984, l='MpServer', x=-175,50, y=51,00, z=-111,50], acn['Squid'/77453, l='MpServer', x=-169,50, y=61,00, z=-201,50], acn['Squid'/77450, l='MpServer', x=-162,50, y=61,00, z=-199,50], acn['Squid'/77451, l='MpServer', x=-163,50, y=61,00, z=-204,50], acn['Squid'/77449, l='MpServer', x=-163,50, y=61,00, z=-203,50], acn['Squid'/77468, l='MpServer', x=-129,50, y=47,00, z=-108,50], acn['Squid'/77543, l='MpServer', x=-135,50, y=59,00, z=-108,50], aca['Rabbit'/76, l='MpServer', x=-201,73, y=69,19, z=-202,25], abz['Pig'/77, l='MpServer', x=-197,50, y=68,00, z=-205,50], abz['Pig'/78, l='MpServer', x=-207,22, y=68,00, z=-206,94], abz['Pig'/79, l='MpServer', x=-196,91, y=69,00, z=-204,00], abz['Pig'/72, l='MpServer', x=-209,97, y=68,00, z=-195,28], aca['Rabbit'/74, l='MpServer', x=-199,66, y=63,00, z=-209,66], aca['Rabbit'/75, l='MpServer', x=-199,81, y=65,32, z=-206,79], abz['Pig'/81, l='MpServer', x=-202,47, y=69,00, z=-195,88], abz['Pig'/80, l='MpServer', x=-195,50, y=68,00, z=-204,50], abz['Pig'/83, l='MpServer', x=-195,53, y=70,00, z=-189,19], abz['Pig'/82, l='MpServer', x=-200,88, y=68,34, z=-193,88], cij['lAngelP'/503, l='MpServer', x=-186,74, y=254,69, z=-171,76], acn['Squid'/75845, l='MpServer', x=-139,50, y=54,00, z=-175,50], acn['Squid'/75844, l='MpServer', x=-139,50, y=54,00, z=-174,50], acn['Squid'/75843, l='MpServer', x=-136,50, y=54,00, z=-176,50], acn['Squid'/75842, l='MpServer', x=-132,50, y=54,00, z=-180,50], acn['Squid'/75862, l='MpServer', x=-133,50, y=51,00, z=-195,50], acn['Squid'/75863, l='MpServer', x=-135,50, y=51,00, z=-198,50], acn['Squid'/75861, l='MpServer', x=-134,50, y=51,00, z=-197,50], acn['Squid'/77367, l='MpServer', x=-124,50, y=54,00, z=-125,50], acn['Squid'/75864, l='MpServer', x=-133,50, y=51,00, z=-197,50], acn['Squid'/77327, l='MpServer', x=-145,50, y=55,00, z=-189,50], acn['Squid'/77326, l='MpServer', x=-145,50, y=55,00, z=-191,50], acn['Squid'/77325, l='MpServer', x=-143,50, y=55,00, z=-189,50], acn['Squid'/77324, l='MpServer', x=-143,50, y=55,00, z=-187,50], ads['Falling Block'/175, l='MpServer', x=-327,50, y=14,09, z=-205,50], ads['Falling Block'/186, l='MpServer', x=-326,50, y=14,09, z=-202,50], ads['Falling Block'/187, l='MpServer', x=-327,50, y=14,09, z=-202,50], ads['Falling Block'/184, l='MpServer', x=-324,50, y=14,09, z=-204,50], ads['Falling Block'/185, l='MpServer', x=-327,50, y=14,09, z=-203,50], ads['Falling Block'/188, l='MpServer', x=-325,50, y=14,09, z=-202,50], ads['Falling Block'/178, l='MpServer', x=-326,50, y=14,09, z=-204,50], ads['Falling Block'/179, l='MpServer', x=-325,50, y=14,09, z=-204,50], ads['Falling Block'/177, l='MpServer', x=-326,50, y=14,09, z=-205,50], ads['Falling Block'/182, l='MpServer', x=-326,50, y=14,09, z=-203,50], ads['Falling Block'/183, l='MpServer', x=-325,50, y=14,09, z=-203,50], ads['Falling Block'/181, l='MpServer', x=-327,50, y=14,09, z=-204,50], acn['Squid'/77379, l='MpServer', x=-131,50, y=57,00, z=-193,50], acn['Squid'/77378, l='MpServer', x=-131,50, y=57,00, z=-196,50], acn['Squid'/77377, l='MpServer', x=-128,50, y=57,00, z=-196,50], acn['Squid'/77380, l='MpServer', x=-130,50, y=57,00, z=-194,50], ads['Falling Block'/274, l='MpServer', x=-277,50, y=9,09, z=-259,50], ads['Falling Block'/9522, l='MpServer', x=-326,50, y=22,20, z=-203,50], ads['Falling Block'/9521, l='MpServer', x=-324,50, y=21,20, z=-205,50], ads['Falling Block'/9520, l='MpServer', x=-325,50, y=22,20, z=-204,50], ads['Falling Block'/9518, l='MpServer', x=-326,50, y=22,20, z=-205,50], ads['Falling Block'/9519, l='MpServer', x=-326,50, y=22,20, z=-204,50], ads['Falling Block'/9517, l='MpServer', x=-325,50, y=21,20, z=-205,50], acn['Squid'/77277, l='MpServer', x=-126,50, y=55,00, z=-220,50], acn['Squid'/75619, l='MpServer', x=-123,50, y=53,00, z=-170,50], acn['Squid'/77276, l='MpServer', x=-129,50, y=55,00, z=-219,50], acn['Squid'/75618, l='MpServer', x=-123,50, y=53,00, z=-167,50], acn['Squid'/77279, l='MpServer', x=-125,50, y=55,00, z=-216,50], acn['Squid'/77278, l='MpServer', x=-128,50, y=55,00, z=-216,50], acn['Squid'/75744, l='MpServer', x=-133,50, y=59,00, z=-142,50], acn['Squid'/75745, l='MpServer', x=-132,50, y=59,00, z=-145,50], acn['Squid'/75743, l='MpServer', x=-132,50, y=59,00, z=-144,50], acn['Squid'/75742, l='MpServer', x=-134,50, y=59,00, z=-141,50]]
Retry entities: 0 total; []
Server brand: vanilla
Server type: Integrated singleplayer server
Stacktrace:
at cei.a(SourceFile:308)
at bsr.b(SourceFile:2255)
at bsr.a(SourceFile:326)
at net.minecraft.client.main.Main.main(SourceFile:120)
-- System Details --
Details:
Minecraft Version: 14w34a
Operating System: Windows 7 (amd64) version 6.1
Java Version: 1.7.0_51, Oracle Corporation
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
Memory: 466760096 bytes (445 MB) / 874512384 bytes (834 MB) up to 3817865216 bytes (3641 MB)
JVM Flags: 2 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx4G
IntCache: cache: 1, tcache: 1, allocated: 12, tallocated: 94
Launched Version: 14w34a
LWJGL: 2.9.1
OpenGL: GeForce GTX 770/PCIe/SSE2 GL version 4.4.0, NVIDIA Corporation
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: Yes
Is Modded: Probably not. Jar signature remains and client brand is untouched.
Type: Client (map_client.txt)
Resource Packs: []
Current Language: English (US)
Profiler Position: N/A (disabled)
Linked issues
is duplicated by 5
Comments

Sorry by that and thanks for report me.
Confirmed, Dev has been poked.