If you try to push blocks over the natural world border, they get glitched and they stay there.

Video that shows how: http://youtu.be/rurEBg16CAY

Crash report:

---- Minecraft Crash Report ----
// I'm sorry, Dave.

Time: 18/08/14 16:48
Description: Manually triggered debug crash

java.lang.Throwable
at bsr.r(SourceFile:1566)
at bsr.as(SourceFile:875)
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 cei.a(SourceFile:308)

– Affected level –
Details:
Level name: MpServer
All players: 1 total; [cij['lAngelP'/193, l='MpServer', x=29999980,34, y=68,00, z=123,89]]
Chunk stats: MultiplayerChunkCache: 589, 589
Level seed: 0
Level generator: ID 00 - default, ver 1. Features enabled: false
Level generator options:
Level spawn location: 8,00,64,00,8,00 - World: (8,64,8), Chunk: (at 8,4,8 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)
Level time: 17096 game time, 17096 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: 62 total; [aft['Skeleton'/357859, l='MpServer', x=29999961,28, y=51,00, z=125,47], agb['Spider'/694272, l='MpServer', x=29999930,00, y=20,00, z=173,50], aft['Skeleton'/616688, l='MpServer', x=29999932,00, y=66,00, z=157,50], abn['Bat'/634183, l='MpServer', x=29999945,69, y=22,22, z=192,69], aft['Skeleton'/707020, l='MpServer', x=29999920,00, y=16,00, z=197,50], aft['Skeleton'/625540, l='MpServer', x=29999912,00, y=65,00, z=132,50], aem['Creeper'/670624, l='MpServer', x=29999960,47, y=72,00, z=95,63], abn['Bat'/638185, l='MpServer', x=29999930,58, y=57,49, z=181,47], aft['Skeleton'/612247, l='MpServer', x=29999951,31, y=70,91, z=121,50], aft['Skeleton'/634908, l='MpServer', x=29999912,00, y=67,00, z=120,50], aft['Skeleton'/620813, l='MpServer', x=29999926,00, y=66,00, z=94,50], aft['Skeleton'/670616, l='MpServer', x=29999955,50, y=72,00, z=97,28], agb['Spider'/322108, l='MpServer', x=29999964,28, y=52,09, z=124,28], aft['Skeleton'/668389, l='MpServer', x=29999964,00, y=67,00, z=184,50], aem['Creeper'/668374, l='MpServer', x=29999910,00, y=57,00, z=198,50], aem['Creeper'/690191, l='MpServer', x=29999904,00, y=72,00, z=183,50], cij['lAngelP'/193, l='MpServer', x=29999980,34, y=68,00, z=123,89], abn['Bat'/688373, l='MpServer', x=29999913,75, y=35,63, z=66,97], abn['Bat'/691224, l='MpServer', x=29999908,96, y=37,23, z=57,49], aem['Creeper'/620685, l='MpServer', x=29999902,00, y=30,00, z=65,50], agb['Spider'/668270, l='MpServer', x=29999938,00, y=66,00, z=184,50], agb['Spider'/668269, l='MpServer', x=29999940,00, y=66,00, z=185,50], agb['Spider'/668276, l='MpServer', x=29999944,00, y=66,00, z=189,50], abn['Bat'/688144, l='MpServer', x=29999965,25, y=46,91, z=101,91], abn['Bat'/697909, l='MpServer', x=29999979,56, y=19,91, z=68,47], agg['Zombie'/632976, l='MpServer', x=29999918,00, y=63,00, z=53,50], agg['Zombie'/612787, l='MpServer', x=29999924,00, y=13,00, z=50,50], abn['Bat'/615996, l='MpServer', x=29999971,54, y=38,15, z=75,63], aem['Creeper'/668121, l='MpServer', x=29999955,47, y=70,91, z=104,34], abn['Bat'/670047, l='MpServer', x=29999932,32, y=40,67, z=152,77], agg['Zombie'/633694, l='MpServer', x=29999960,00, y=19,00, z=54,50], aft['Skeleton'/671045, l='MpServer', x=29999904,00, y=68,00, z=116,50], agg['Zombie'/691033, l='MpServer', x=29999964,31, y=66,02, z=192,50], aem['Creeper'/691036, l='MpServer', x=29999960,47, y=67,16, z=192,47], aft['Skeleton'/686501, l='MpServer', x=29999938,00, y=21,00, z=117,50], aft['Skeleton'/686504, l='MpServer', x=29999940,00, y=21,00, z=117,50], aem['Creeper'/671091, l='MpServer', x=29999932,00, y=67,00, z=102,50], aem['Creeper'/671098, l='MpServer', x=29999932,00, y=67,00, z=108,50], aft['Skeleton'/668012, l='MpServer', x=29999928,75, y=12,00, z=182,22], agb['Spider'/340941, l='MpServer', x=29999961,27, y=51,00, z=126,75], agb['Spider'/340939, l='MpServer', x=29999960,28, y=52,09, z=129,28], aft['Skeleton'/688991, l='MpServer', x=29999960,00, y=34,00, z=54,50], agb['Spider'/633752, l='MpServer', x=29999932,00, y=37,00, z=97,50], aem['Creeper'/212654, l='MpServer', x=29999967,47, y=46,00, z=103,97], agg['Zombie'/622721, l='MpServer', x=29999964,00, y=19,00, z=54,50], agg['Zombie'/707249, l='MpServer', x=29999904,00, y=28,02, z=183,50], abn['Bat'/670814, l='MpServer', x=29999970,84, y=38,14, z=75,47], adt['item.item.dyePowder.black'/593206, l='MpServer', x=29999924,69, y=62,00, z=67,88], abn['Bat'/670822, l='MpServer', x=29999974,77, y=37,00, z=71,45], agg['Zombie'/616359, l='MpServer', x=29999906,66, y=66,00, z=153,19], agb['Spider'/645412, l='MpServer', x=29999974,78, y=66,97, z=136,41], agb['Spider'/645410, l='MpServer', x=29999978,55, y=65,91, z=154,26], abn['Bat'/643468, l='MpServer', x=29999910,88, y=13,49, z=165,09], aem['Creeper'/645387, l='MpServer', x=29999932,00, y=37,00, z=139,50], abn['Bat'/643473, l='MpServer', x=29999923,68, y=12,17, z=176,54], abn['Bat'/670934, l='MpServer', x=29999975,75, y=25,09, z=57,25], aft['Skeleton'/627055, l='MpServer', x=29999904,00, y=30,00, z=65,50], aem['Creeper'/673665, l='MpServer', x=29999940,00, y=54,00, z=171,50], aeo['Enderman'/690937, l='MpServer', x=29999918,00, y=66,00, z=128,50], abn['Bat'/667087, l='MpServer', x=29999970,23, y=22,13, z=42,22], aft['Skeleton'/690931, l='MpServer', x=29999914,00, y=66,00, z=124,50], aft['Skeleton'/613406, l='MpServer', x=29999924,00, y=67,00, z=127,50]]
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:321)
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: 1105419736 bytes (1054 MB) / 1711276032 bytes (1632 MB) up to 3817865216 bytes (3641 MB)
JVM Flags: 2 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx4G
IntCache: cache: 0, tcache: 0, 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)