End Crash

Going to the End randomly crashes, with this report;

Minecraft has crashed!      
      ----------------------      

Minecraft has stopped running because it encountered a problem; Ticking entity
A full error report has been saved to C:\Users\Administrator1\AppData\Roaming\.minecraft\crash-reports\crash-2012-11-03_09.41.23-server.txt for your convenience. Please include a copy of that file (Not this screen!) if you report this crash to anyone; without it, they will not be able to help fix the crash :(



--- BEGIN ERROR REPORT 1824fb5d --------
Full report at:
C:\Users\Administrator1\AppData\Roaming\.minecraft\crash-reports\crash-2012-11-03_09.41.23-server.txt

java.lang.IllegalStateException: Entity is already tracked!
	at ih.a(SourceFile:72)
	at ih.a(SourceFile:56)
	at ii.a(SourceFile:24)
	at xv.a(SourceFile:842)
	at im.a(SourceFile:580)
	at xv.d(SourceFile:834)
	at gl.a(SourceFile:367)
	at lp.b(SourceFile:1484)
	at amg.a(SourceFile:62)
	at lp.D(SourceFile:645)
	at lp.d(SourceFile:608)
	at mc.e(SourceFile:932)
	at mc.c(SourceFile:1130)
	at lm.c(SourceFile:42)
	at oy.c(SourceFile:33)
	at oz.c(SourceFile:45)
	at mc.j_(SourceFile:524)
	at xv.a(SourceFile:1315)
	at im.a(SourceFile:451)
	at xv.g(SourceFile:1294)
	at xv.h(SourceFile:1194)
	at im.h(SourceFile:363)
	at net.minecraft.server.MinecraftServer.r(SourceFile:750)
	at net.minecraft.server.MinecraftServer.q(SourceFile:685)
	at bdh.q(SourceFile:117)
	at net.minecraft.server.MinecraftServer.run(SourceFile:619)
	at fx.run(SourceFile:855)
--- END ERROR REPORT e2d066ed ----------