You can get the same issue with redo, it seems to be caused by sections that cross uninitialized chunks. It's unable to undo or redo those sections without crashing
{F6922}
```[2016-03-27 16:47:16] java.lang.NullPointerException: Exception: REQUESTED TYPE 0 IS NULL
[2016-03-27 16:47:16] at org.schema.game.common.data.element.ElementKeyMap.getInfo(SourceFile:596)
[2016-03-27 16:47:16] at obfuscated.cR.a(SourceFile:45)
[2016-03-27 16:47:16] at org.schema.game.common.controller.EditableSendableSegmentController.redo(SourceFile:2332)
[2016-03-27 16:47:16] at obfuscated.ds.h(SourceFile:1815)
[2016-03-27 16:47:16] at obfuscated.da.f(SourceFile:163)
[2016-03-27 16:47:16] at obfuscated.oh.callback(SourceFile:849)
[2016-03-27 16:47:16] at org.schema.schine.network.client.GUICallbackController.execute(SourceFile:40)
[2016-03-27 16:47:16] at obfuscated.C.updateStateInput(SourceFile:1365)
[2016-03-27 16:47:16] at obfuscated.avy.a(SourceFile:1167)
[2016-03-27 16:47:16] at obfuscated.C.h(SourceFile:2866)
[2016-03-27 16:47:16] at obfuscated.QF.run(SourceFile:92)
[2016-03-27 16:47:16] at java.lang.Thread.run(Unknown Source)```