[MC-502] IllegalStateException::Entity is already tracked!

Entered the End portal in my world and, upon loading the End, game immediately crashed. Subsequent attempts to load the world result in the client crashing before anything is loaded. Crash report is included below.
--- BEGIN ERROR REPORT 710795e4 --------
Generated 10/25/12 10:34 AM

- Minecraft Version: 1.4.2
- Operating System: Windows 7 (amd64) version 6.1
- Java Version: 1.7.0_09, Oracle Corporation
- Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
- Memory: 471753064 bytes (449 MB) / 648740864 bytes (618 MB) up to 954466304 bytes (910 MB)
- JVM Flags: 2 total; -Xms512m -Xmx1024m
- AABB Pool Size: 3662 (205072 bytes; 0 MB) allocated, 3662 (205072 bytes; 0 MB) used
- Is Modded: Probably not
- Profiler Position: N/A (disabled)
- Vec3 Pool Size: 811 (45416 bytes; 0 MB) allocated, 811 (45416 bytes; 0 MB) used
- Player Count: 1 / 8; [ih['Feanarang'/5839, l='LP world?', x=100.00, y=49.00, z=0.00]]
- World LP world? Entities: 88 total; [pm['Enderman'/5840, l='LP world?', x=97.18, y=35.00, z=2.98], pm['Enderman'/5841, l='LP world?', x=101.50, y=34.00, z=9.50], ih['Feanarang'/5839, l='LP world?', x=100.00, y=49.00, z=0.00], pm['Enderman'/5844, l='LP world?', x=-51.41, y=57.00, z=11.96], pm['Enderman'/5846, l='LP world?', x=-42.50, y=58.00, z=12.50], pm['Enderman'/5847, l='LP world?', x=-24.50, y=62.00, z=-21.54], pm['Enderman'/5848, l='LP world?', x=-24.50, y=62.00, z=-20.65], pm['Enderman'/5849, l='LP world?', x=-24.50, y=63.00, z=-17.84], ox['entity.EnderCrystal.name'/5850, l='LP world?', x=-26.50, y=60.00, z=110.50], pm['Enderman'/5851, l='LP world?', x=14.54, y=36.00, z=-87.09], pm['Enderman'/5852, l='LP world?', x=12.53, y=62.00, z=24.58], pm['Enderman'/5853, l='LP world?', x=6.95, y=59.00, z=59.92], pm['Enderman'/5854, l='LP world?', x=5.79, y=59.00, z=60.51], pm['Enderman'/5855, l='LP world?', x=4.39, y=58.00, z=65.01], pm['Enderman'/5856, l='LP world?', x=22.50, y=42.00, z=-83.50], pm['Enderman'/5857, l='LP world?', x=24.50, y=52.00, z=84.50], pm['Enderman'/5858, l='LP world?', x=31.50, y=52.00, z=80.50], pm['Enderman'/5859, l='LP world?', x=40.50, y=55.00, z=-88.50], pm['Enderman'/5860, l='LP world?', x=42.50, y=60.00, z=-17.50], pm['Enderman'/5861, l='LP world?', x=43.34, y=60.00, z=-17.32], pm['Enderman'/5862, l='LP world?', x=36.47, y=61.00, z=-18.70], pm['Enderman'/5863, l='LP world?', x=38.50, y=61.00, z=-16.50], pm['Enderman'/5864, l='LP world?', x=36.83, y=61.00, z=-19.58], pm['Enderman'/5865, l='LP world?', x=39.50, y=61.00, z=-22.50], pm['Enderman'/5866, l='LP world?', x=37.21, y=61.00, z=-9.73], pm['Enderman'/5867, l='LP world?', x=43.50, y=60.00, z=-14.50], pm['Enderman'/5868, l='LP world?', x=44.53, y=60.00, z=-11.16], pm['Enderman'/5869, l='LP world?', x=37.87, y=61.00, z=-15.46], pm['Enderman'/5870, l='LP world?', x=35.50, y=63.00, z=56.45], pm['Enderman'/5871, l='LP world?', x=61.50, y=57.00, z=-79.54], pm['Enderman'/5872, l='LP world?', x=49.37, y=60.00, z=-13.09], pm['Enderman'/5873, l='LP world?', x=58.42, y=59.00, z=-4.22], pm['Enderman'/5874, l='LP world?', x=63.66, y=60.00, z=-15.31], pm['Enderman'/5875, l='LP world?', x=61.79, y=59.00, z=0.76], pm['Enderman'/5876, l='LP world?', x=54.12, y=61.00, z=21.53], pm['Enderman'/5877, l='LP world?', x=57.03, y=61.00, z=23.60], pm['Enderman'/5878, l='LP world?', x=53.43, y=62.00, z=31.27], pm['Enderman'/5879, l='LP world?', x=60.18, y=61.00, z=33.94], pm['Enderman'/5880, l='LP world?', x=57.50, y=34.00, z=94.50], pm['Enderman'/5881, l='LP world?', x=57.72, y=34.00, z=91.49], pm['Enderman'/5882, l='LP world?', x=71.04, y=58.00, z=-31.59], pm['Enderman'/5883, l='LP world?', x=72.46, y=58.00, z=-31.53], pm['Enderman'/5884, l='LP world?', x=70.50, y=58.00, z=-29.95], pm['Enderman'/5885, l='LP world?', x=70.48, y=58.00, z=-30.79], pm['Enderman'/5886, l='LP world?', x=67.41, y=59.00, z=-12.26], pm['Enderman'/5887, l='LP world?', x=78.60, y=59.00, z=-5.03], pm['Enderman'/5888, l='LP world?', x=73.45, y=59.00, z=-6.53], pm['Enderman'/5889, l='LP world?', x=67.07, y=59.00, z=-13.12], pm['Enderman'/5890, l='LP world?', x=71.77, y=58.00, z=30.71], pm['Enderman'/5891, l='LP world?', x=70.41, y=60.00, z=16.21], pm['Enderman'/5892, l='LP world?', x=71.27, y=60.00, z=16.29], pg['item.tile.stonebrick'/5893, l='LP world?', x=100.00, y=50.09, z=0.00], pg['item.tile.stonebrick'/5894, l='LP world?', x=100.00, y=50.13, z=0.00], pm['Enderman'/5895, l='LP world?', x=77.45, y=36.00, z=52.14], pm['Enderman'/5896, l='LP world?', x=64.35, y=57.00, z=49.92], pm['Enderman'/5897, l='LP world?', x=82.66, y=54.00, z=-55.89], pm['Enderman'/5898, l='LP world?', x=80.82, y=55.00, z=-53.50], pm['Enderman'/5899, l='LP world?', x=82.30, y=57.00, z=-44.05], pm['Enderman'/5900, l='LP world?', x=94.68, y=57.00, z=-19.51], pm['Enderman'/5901, l='LP world?', x=82.60, y=59.00, z=-6.54], pm['Enderman'/5902, l='LP world?', x=91.68, y=57.00, z=-15.55], pm['Enderman'/5903, l='LP world?', x=88.67, y=59.92, z=-0.37], pm['Enderman'/5904, l='LP world?', x=95.66, y=59.00, z=-9.70], pm['Enderman'/5905, l='LP world?', x=84.38, y=39.00, z=0.18], pm['Enderman'/5906, l='LP world?', x=92.49, y=59.00, z=6.75], pm['Enderman'/5907, l='LP world?', x=81.26, y=60.00, z=9.83], pm['Enderman'/5908, l='LP world?', x=88.83, y=60.00, z=4.55], pm['Enderman'/5909, l='LP world?', x=81.17, y=60.00, z=7.81], pm['Enderman'/5910, l='LP world?', x=86.02, y=59.00, z=0.55], pm['Enderman'/5911, l='LP world?', x=85.77, y=58.00, z=26.27], pm['Enderman'/5912, l='LP world?', x=86.75, y=59.00, z=20.43], pm['Enderman'/5913, l='LP world?', x=82.18, y=59.00, z=19.34], pm['Enderman'/5914, l='LP world?', x=84.01, y=58.00, z=27.58], pm['Enderman'/5915, l='LP world?', x=81.65, y=45.00, z=44.15], pm['Enderman'/5916, l='LP world?', x=87.78, y=58.00, z=33.57], pm['Enderman'/5917, l='LP world?', x=106.33, y=57.00, z=-35.10], pm['Enderman'/5918, l='LP world?', x=99.04, y=57.00, z=-18.29], pm['Enderman'/5919, l='LP world?', x=106.98, y=58.00, z=-17.63], pm['Enderman'/5920, l='LP world?', x=98.57, y=33.00, z=-4.03], pm['Enderman'/5921, l='LP world?', x=98.43, y=59.00, z=-3.51], pm['Enderman'/5922, l='LP world?', x=96.96, y=59.00, z=-8.04], pm['Enderman'/5923, l='LP world?', x=97.52, y=59.00, z=-7.24], pm['Enderman'/5924, l='LP world?', x=115.38, y=46.00, z=-68.08], pm['Enderman'/5925, l='LP world?', x=123.27, y=46.00, z=-60.39], pm['Enderman'/5926, l='LP world?', x=125.32, y=45.00, z=-54.44], pm['Enderman'/5927, l='LP world?', x=125.93, y=45.00, z=-60.53], pm['Enderman'/5928, l='LP world?', x=116.94, y=57.00, z=-2.59], pg['item.tile.stonebrick'/5894, l='LP world?', x=100.00, y=50.13, z=0.00]]
- World LP world? Players: 1 total; [ih['Feanarang'/5839, l='LP world?', x=100.00, y=49.00, z=0.00]]
- World LP world? Chunk Stats: ServerChunkCache: 441 Drop: 0
- Type: Integrated Server

java.lang.IllegalStateException: Entity is already tracked!
	at hz.a(SourceFile:67)
	at hz.a(SourceFile:45)
	at ia.a(SourceFile:24)
	at xe.a(SourceFile:786)
	at ie.a(SourceFile:553)
	at xe.d(SourceFile:778)
	at ge.a(SourceFile:355)
	at lb.b(SourceFile:1442)
	at alc.a(SourceFile:62)
	at lb.D(SourceFile:659)
	at lb.d(SourceFile:622)
	at pg.j_(SourceFile:69)
	at xe.a(SourceFile:1218)
	at ie.a(SourceFile:424)
	at xe.g(SourceFile:1197)
	at xe.h(SourceFile:1122)
	at ie.h(SourceFile:352)
	at net.minecraft.server.MinecraftServer.r(SourceFile:718)
	at net.minecraft.server.MinecraftServer.q(SourceFile:661)
	at bcb.q(SourceFile:117)
	at net.minecraft.server.MinecraftServer.run(SourceFile:595)
	at fp.run(SourceFile:818)
--- END ERROR REPORT 1738cac4 ----------
Thank you for looking into this!
EDIT:
After several attempts at entering the world, I was able to enter it successfully, spawning on the entrance platform in the End, which is where I should be. Still not sure what caused the crash in the first place.