14w20b: World Generation Crash

I wanted to play with the latest snapshot features for world generation, so I
went to generate a custom world. I entered in all the settings I wanted, and clicked "Done". I realized I had forgotten something, so I clicked "Customize" again. The game instantly crashed. I entered it all in again, and copy/pasted the preset info. Then I pressed "Done" in the Preset settings. I crashed again.
Each time I crashed, I got a report that looked something like this:

---- Minecraft Crash Report ----
// You're mean.

Time: 5/22/14 12:46 PM
Description: Updating screen events

java.lang.NullPointerException: Updating screen events
	at bmx.b(SourceFile:497)
	at bmx.a(SourceFile:453)
	at bll.e(SourceFile:53)
	at bll.<init>(SourceFile:25)
	at bly.a(SourceFile:163)
	at bly.a(SourceFile:137)
	at bly.r(SourceFile:41)
	at bly.<init>(SourceFile:32)
	at bmx.g(SourceFile:362)
	at bmx.s_(SourceFile:220)
	at bnt.a(SourceFile:205)
	at bjs.a(SourceFile:730)
	at bmu.a(SourceFile:118)
	at bnt.a(SourceFile:180)
	at bmu.a(SourceFile:103)
	at bnt.d(SourceFile:242)
	at bmu.d(SourceFile:91)
	at bnt.k(SourceFile:219)
	at bjs.p(SourceFile:1432)
	at bjs.ah(SourceFile:843)
	at bjs.f(SourceFile:797)
	at net.minecraft.client.main.Main.main(SourceFile:121)


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

-- Head --
Stacktrace:
	at bmx.b(SourceFile:497)
	at bmx.a(SourceFile:453)
	at bll.e(SourceFile:53)
	at bll.<init>(SourceFile:25)
	at bly.a(SourceFile:163)
	at bly.a(SourceFile:137)
	at bly.r(SourceFile:41)
	at bly.<init>(SourceFile:32)
	at bmx.g(SourceFile:362)
	at bmx.s_(SourceFile:220)
	at bnt.a(SourceFile:205)
	at bjs.a(SourceFile:730)
	at bmu.a(SourceFile:118)
	at bnt.a(SourceFile:180)
	at bmu.a(SourceFile:103)
	at bnt.d(SourceFile:242)
	at bmu.d(SourceFile:91)
	at bnt.k(SourceFile:219)

-- Affected screen --
Details:
	Screen name: bmx
Stacktrace:
	at bjs.p(SourceFile:1432)
	at bjs.ah(SourceFile:843)
	at bjs.f(SourceFile:797)
	at net.minecraft.client.main.Main.main(SourceFile:121)

-- System Details --
Details:
	Minecraft Version: 14w21b
	Operating System: Windows Vista (amd64) version 6.0
	Java Version: 1.8.0_05, Oracle Corporation
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
	Memory: 26615048 bytes (25 MB) / 177209344 bytes (169 MB) up to 954728448 bytes (910 MB)
	JVM Flags: 2 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx1G
	IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
	Launched Version: 14w21b
	LWJGL: 2.9.1
	OpenGL: GeForce GTX 650/PCIe/SSE2 GL version 4.3.0, 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.
Anisotropic filtering is supported and maximum anisotropy is 16.
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: [Better Than Default!, Awesome Swords!]
	Current Language: English (US)
	Profiler Position: N/A (disabled)
	Anisotropic Filtering: Off (1)

Also, in case this helps, here is the preset I am trying oh-so-hard to use:

{"coordinateScale":684.412,"heightScale":684.412,"lowerLimitScale":512.0,"upperLimitScale":512.0,"depthNoiseScaleX":200.0,"depthNoiseScaleZ":200.0,"depthNoiseScaleExponent":0.5,"mainNoiseScaleX":80.0,"mainNoiseScaleY":160.0,"mainNoiseScaleZ":80.0,"baseSize":8.5,"stretchY":12.0,"biomeDepthWeight":1.0,"biomeDepthOffset":0.0,"biomeScaleWeight":1.0,"biomeScaleOffset":0.0,"seaLevel":63,"useCaves":true,"useDungeons":true,"dungeonChance":50,"useStrongholds":true,"useVillages":true,"useMineShafts":true,"useTemples":true,"useRavines":true,"useWaterLakes":true,"waterLakeChance":4,"useLavaLakes":true,"lavaLakeChance":80,"useLavaOceans":false,"fixedBiome":37,"biomeSize":4,"riverSize":4,"dirtSize":25,"dirtCount":10,"dirtMinHeight":0,"dirtMaxHeight":256,"gravelSize":20,"gravelCount":10,"gravelMinHeight":0,"gravelMaxHeight":256,"graniteSize":35,"graniteCount":15,"graniteMinHeight":0,"graniteMaxHeight":150,"dioriteSize":35,"dioriteCount":15,"dioriteMinHeight":0,"dioriteMaxHeight":150,"andesiteSize":35,"andesiteCount":15,"andesiteMinHeight":0,"andesiteMaxHeight":150,"coalSize":25,"coalCount":20,"coalMinHeight":0,"coalMaxHeight":150,"ironSize":25,"ironCount":20,"ironMinHeight":0,"ironMaxHeight":100,"goldSize":20,"goldCount":10,"goldMinHeight":0,"goldMaxHeight":70,"redstoneSize":15,"redstoneCount":10,"redstoneMinHeight":0,"redstoneMaxHeight":30,"diamondSize":15,"diamondCount":10,"diamondMinHeight":0,"diamondMaxHeight":30,"lapisSize":10,"lapisCount":5,"lapisCenterHeight":16,"lapisSpread":16}

I also discovered that this still exists in 14w21a and b...

Hope this helps,

The Fury Artist.