Note
The exact reason why this happens is unknown. This bug cannot be reproduced in 1.9. This crash was first mentioned for a normal Survival world in this comment.
The bug
Having many hoppers pointing into each other crashes the game. This crash is caused by a java.util.ConcurrentModificationException
(see attached crash report).
How to reproduce
Create a Superflat world with the preset
3;minecraft:hopper:2;1;
1.9.3-pre1
Description: Batching chunks
java.util.ConcurrentModificationException
at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:901)
at java.util.ArrayList$Itr.next(ArrayList.java:851)
at aht.a(SourceFile:1858)
at ase.a(SourceFile:634)
at aic.r(SourceFile:63)
at bqb.b(SourceFile:160)
at bpx.a(SourceFile:100)
at bpx.run(SourceFile:43)
at java.lang.Thread.run(Thread.java:745)
Still an issue in 1.9.3-pre2?