The following is a crash report I received after testing the latest snapshot. I wouldn't normally worry about it, but from what I could tell, it said something about world generation and chests. I don't know for sure, but it's what I could figure out. (Also, I don't know if anyone else has published this particular stash report. Although I did check, I couldn't tell for sure if it was the same crash report.)

---- Minecraft Crash Report ----
// Surprise! Haha. Well, this is awkward.

Time: 7/2/14 10:33 AM
Description: Rendering entity in world

java.lang.IllegalArgumentException: Cannot set property azi

{name=facing, clazz=class dw, values=[north, south, west, east]}

to down on block minecraft:chest, it is not an allowed value
at ayx.a(SourceFile:132)
at apr.b(SourceFile:425)
at cfb.a(SourceFile:85)
at cfb.a(SourceFile:113)
at cjg.a(SourceFile:116)
at cjg.a(SourceFile:95)
at cjg.a(SourceFile:15)
at cic.a(SourceFile:272)
at cic.a(SourceFile:237)
at cic.a(SourceFile:204)
at cei.a(SourceFile:501)
at cdo.a(SourceFile:1194)
at cdo.a(SourceFile:1121)
at cdo.b(SourceFile:973)
at bmi.ap(SourceFile:886)
at bmi.a(SourceFile:303)
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 ayx.a(SourceFile:132)
at apr.b(SourceFile:425)
at cfb.a(SourceFile:85)
at cfb.a(SourceFile:113)
at cjg.a(SourceFile:116)
at cjg.a(SourceFile:95)
at cjg.a(SourceFile:15)

– Entity being rendered –
Details:
Entity Type: MinecartChest (aat)
Entity ID: 126397
Entity Name: container.minecart
Entity's Exact location: -281.50, 32.06, 341.50
Entity's Block location: -282.00,32.00,341.00 - World: (-282,32,341), Chunk: (at 6,2,5 in -18,21; contains blocks -288,0,336 to -273,255,351), Region: (-1,0; contains chunks -32,0 to -1,31, blocks -512,0,0 to -1,255,511)
Entity's Momentum: 0.00, 0.00, 0.00
Entity's Rider: ~_ERROR~ NullPointerException: null
Entity's Vehicle: ~_ERROR~ NullPointerException: null

– Renderer details –
Details:
Assigned renderer: cjg@24fc5248
Location: -19.37,-53.32,-0.10 - World: (-20,-54,-1), Chunk: (at 12,-4,15 in -2,-1; contains blocks -32,0,-16 to -17,255,-1), Region: (-1,-1; contains chunks -32,-32 to -1,-1, blocks -512,0,-512 to -1,255,-1)
Rotation: 0.0
Delta: 0.25450897
Stacktrace:
at cic.a(SourceFile:272)
at cic.a(SourceFile:237)
at cic.a(SourceFile:204)
at cei.a(SourceFile:501)
at cdo.a(SourceFile:1194)
at cdo.a(SourceFile:1121)

– Affected level –
Details:
Level name: MpServer
All players: 1 total; [ccy['jd0g12'/316, l='MpServer', x=-262.24, y=85.10, z=341.45]]
Chunk stats: MultiplayerChunkCache: 385, 385
Level seed: 0
Level generator: ID 00 - default, ver 1. Features enabled: false
Level generator options:
Level spawn location: -96.00,64.00,252.00 - World: (-96,64,252), Chunk: (at 0,4,12 in -6,15; contains blocks -96,0,240 to -81,255,255), Region: (-1,0; contains chunks -32,0 to -1,31, blocks -512,0,0 to -1,255,511)
Level time: 7323 game time, 7323 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: 100 total; [acm['Skeleton'/156398, l='MpServer', x=-322.50, y=29.00, z=320.50], acm['Skeleton'/156397, l='MpServer', x=-321.50, y=29.00, z=322.50], zl['Rabbit'/42, l='MpServer', x=-251.41, y=70.00, z=406.84], zl['Rabbit'/40, l='MpServer', x=-251.56, y=70.00, z=408.13], zl['Rabbit'/41, l='MpServer', x=-249.50, y=70.00, z=407.53], aap['item.tile.torch'/55, l='MpServer', x=-247.72, y=29.00, z=339.75], aat['container.minecart'/54, l='MpServer', x=-233.50, y=28.06, z=326.50], aat['container.minecart'/57, l='MpServer', x=-231.50, y=32.06, z=309.50], aat['container.minecart'/56, l='MpServer', x=-240.50, y=29.06, z=330.50], acm['Skeleton'/156401, l='MpServer', x=-323.50, y=29.00, z=320.50], acm['Skeleton'/145244, l='MpServer', x=-183.50, y=30.00, z=360.50], aap['item.tile.gravel'/15185, l='MpServer', x=-251.63, y=32.00, z=382.13], acz['Zombie'/154015, l='MpServer', x=-311.50, y=34.00, z=336.50], zt['Sheep'/126399, l='MpServer', x=-266.47, y=76.00, z=289.91], zt['Sheep'/126398, l='MpServer', x=-273.91, y=72.00, z=285.09], aat['container.minecart'/126397, l='MpServer', x=-281.50, y=32.06, z=341.50], aap['item.tile.torch'/126396, l='MpServer', x=-272.78, y=35.00, z=342.00], aap['item.tile.torch'/126395, l='MpServer', x=-274.31, y=42.00, z=366.28], aat['container.minecart'/126394, l='MpServer', x=-279.50, y=35.06, z=313.50], zt['Sheep'/126400, l='MpServer', x=-273.50, y=70.00, z=290.50], acu['Spider'/149936, l='MpServer', x=-223.50, y=32.00, z=267.50], acy['Witch'/143142, l='MpServer', x=-252.50, y=14.00, z=297.50], acy['Witch'/143143, l='MpServer', x=-253.50, y=14.00, z=297.50], zt['Sheep'/137082, l='MpServer', x=-327.50, y=81.00, z=308.50], zt['Sheep'/137083, l='MpServer', x=-318.13, y=66.00, z=279.81], zt['Sheep'/137080, l='MpServer', x=-326.50, y=81.00, z=311.50], zt['Sheep'/137081, l='MpServer', x=-328.06, y=81.00, z=300.06], zt['Sheep'/137086, l='MpServer', x=-323.56, y=64.00, z=286.19], zt['Sheep'/137084, l='MpServer', x=-323.97, y=65.00, z=282.88], zt['Sheep'/137085, l='MpServer', x=-320.66, y=64.00, z=284.78], aat['container.minecart'/137074, l='MpServer', x=-325.50, y=32.06, z=350.50], zt['Sheep'/137079, l='MpServer', x=-325.56, y=81.00, z=309.53], acz['Zombie'/134850, l='MpServer', x=-191.50, y=32.00, z=348.50], acz['Zombie'/169598, l='MpServer', x=-259.50, y=37.02, z=314.50], abh['Creeper'/157784, l='MpServer', x=-262.50, y=63.00, z=314.50], acz['Zombie'/157786, l='MpServer', x=-265.50, y=63.00, z=313.50], abh['Creeper'/150054, l='MpServer', x=-290.69, y=32.56, z=349.50], acm['Skeleton'/150060, l='MpServer', x=-287.91, y=35.00, z=349.47], abh['Creeper'/121895, l='MpServer', x=-211.50, y=28.00, z=332.50], acm['Skeleton'/121901, l='MpServer', x=-212.50, y=28.00, z=332.50], abh['Creeper'/121897, l='MpServer', x=-212.50, y=28.00, z=330.50], zt['Sheep'/98271, l='MpServer', x=-266.50, y=72.00, z=271.50], aat['container.minecart'/98266, l='MpServer', x=-256.50, y=30.06, z=357.50], acu['Spider'/148070, l='MpServer', x=-287.97, y=70.00, z=265.50], abh['Creeper'/148076, l='MpServer', x=-285.50, y=70.00, z=264.50], abh['Creeper'/148074, l='MpServer', x=-284.50, y=70.00, z=264.50], abh['Creeper'/148075, l='MpServer', x=-285.94, y=70.00, z=265.50], zl['Rabbit'/98279, l='MpServer', x=-256.47, y=73.00, z=387.69], zl['Rabbit'/98278, l='MpServer', x=-262.53, y=70.00, z=387.44], aat['container.minecart'/98277, l='MpServer', x=-258.50, y=38.06, z=385.50], zl['Rabbit'/98276, l='MpServer', x=-257.53, y=71.00, z=383.44], zt['Sheep'/98275, l='MpServer', x=-270.50, y=74.00, z=286.50], zt['Sheep'/98274, l='MpServer', x=-264.50, y=73.00, z=273.50], zt['Sheep'/98273, l='MpServer', x=-265.56, y=73.00, z=275.50], zt['Sheep'/98272, l='MpServer', x=-264.47, y=74.00, z=275.50], acu['Spider'/146633, l='MpServer', x=-300.50, y=39.00, z=288.50], acm['Skeleton'/152097, l='MpServer', x=-245.81, y=33.00, z=365.38], acm['Skeleton'/152099, l='MpServer', x=-244.50, y=33.00, z=359.50], zt['Sheep'/135000, l='MpServer', x=-302.50, y=80.00, z=265.50], aap['item.tile.torch'/135005, l='MpServer', x=-309.72, y=34.00, z=327.81], aat['container.minecart'/135006, l='MpServer', x=-296.50, y=33.06, z=343.50], zt['Sheep'/134997, l='MpServer', x=-306.47, y=67.00, z=267.78], zt['Sheep'/134999, l='MpServer', x=-304.50, y=80.00, z=265.50], zt['Sheep'/134998, l='MpServer', x=-303.38, y=64.00, z=274.44], acm['Skeleton'/152094, l='MpServer', x=-247.50, y=33.00, z=366.50], acm['Skeleton'/152093, l='MpServer', x=-247.50, y=33.00, z=361.50], acm['Skeleton'/170114, l='MpServer', x=-294.50, y=69.02, z=263.50], acm['Skeleton'/170113, l='MpServer', x=-292.50, y=69.02, z=264.50], yz['Bat'/154987, l='MpServer', x=-322.57, y=28.01, z=346.00], ccy['jd0g12'/316, l='MpServer', x=-262.24, y=85.10, z=341.45], acz['Zombie'/131101, l='MpServer', x=-186.50, y=40.00, z=347.50], yz['Bat'/141917, l='MpServer', x=-281.53, y=32.05, z=343.49], yz['Bat'/141916, l='MpServer', x=-259.25, y=33.03, z=340.25], abh['Creeper'/150764, l='MpServer', x=-233.50, y=33.00, z=357.50], abh['Creeper'/150766, l='MpServer', x=-232.50, y=33.00, z=358.50], acz['Zombie'/146261, l='MpServer', x=-267.50, y=29.00, z=271.50], acz['Zombie'/170108, l='MpServer', x=-291.50, y=69.02, z=263.50], abh['Creeper'/154646, l='MpServer', x=-288.50, y=37.00, z=362.50], acz['Zombie'/140087, l='MpServer', x=-259.91, y=39.00, z=349.38], acz['Zombie'/140086, l='MpServer', x=-265.63, y=39.00, z=348.31], acu['Spider'/140095, l='MpServer', x=-254.50, y=39.00, z=343.50], yz['Bat'/143890, l='MpServer', x=-277.13, y=33.10, z=343.25], acm['Skeleton'/142189, l='MpServer', x=-283.50, y=32.00, z=382.50], aap['item.tile.torch'/127292, l='MpServer', x=-293.13, y=39.00, z=364.03], aat['container.minecart'/127291, l='MpServer', x=-284.50, y=32.06, z=374.50], yz['Bat'/149189, l='MpServer', x=-257.47, y=33.00, z=323.13], acu['Spider'/153536, l='MpServer', x=-284.50, y=43.00, z=353.50], zt['Sheep'/139283, l='MpServer', x=-338.22, y=79.00, z=294.50], zt['Sheep'/139282, l='MpServer', x=-337.50, y=79.00, z=292.50], zt['Sheep'/139285, l='MpServer', x=-341.50, y=77.00, z=291.50], zt['Sheep'/139284, l='MpServer', x=-339.56, y=79.00, z=294.50], aat['container.minecart'/139293, l='MpServer', x=-332.50, y=30.06, z=330.50], yz['Bat'/149181, l='MpServer', x=-255.66, y=33.16, z=319.38], abh['Creeper'/145608, l='MpServer', x=-295.34, y=33.00, z=340.66], acm['Skeleton'/145604, l='MpServer', x=-288.06, y=31.00, z=330.28], aap['item.tile.gravel'/13401, l='MpServer', x=-251.81, y=33.00, z=345.06], abj['Enderman'/159118, l='MpServer', x=-284.72, y=31.00, z=354.88], acm['Skeleton'/143588, l='MpServer', x=-255.84, y=36.00, z=324.53], acu['Spider'/159124, l='MpServer', x=-283.56, y=31.00, z=351.31], acu['Spider'/159122, l='MpServer', x=-283.34, y=31.00, z=353.09]]
Retry entities: 0 total; []
Server brand: vanilla
Server type: Integrated singleplayer server
Stacktrace:
at bza.a(SourceFile:310)
at bmi.b(SourceFile:2135)
at bmi.a(SourceFile:312)
at net.minecraft.client.main.Main.main(SourceFile:120)

– System Details –
Details:
Minecraft Version: 14w27a
Operating System: Mac OS X (x86_64) version 10.9.3
Java Version: 1.6.0_65, Apple Inc.
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Apple Inc.
Memory: 155328456 bytes (148 MB) / 444747776 bytes (424 MB) up to 1065025536 bytes (1015 MB)
JVM Flags: 1 total; -Xmx1G
IntCache: cache: 0, tcache: 0, allocated: 13, tallocated: 95
Launched Version: 14w27a
LWJGL: 2.9.1
OpenGL: ATI Radeon HD 5670 OpenGL Engine GL version 2.1 ATI-1.22.25, ATI Technologies Inc.
GL Caps: Using GL 1.3 multitexturing.
Using GL 1.3 texture combiners.
Using framebuffer objects because ARB_framebuffer_object is supported and separate blending is supported.
Shaders are available because OpenGL 2.1 is supported.

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)