In this scenario, the tree nodes for the ace:tree are being built from a list of objects. When the tree is displayed an ArrayIndexOutOfBoundsException is thrown when expanding the 3rd level node.

Looking at how the list is made for the nodes, everything seems to be fine and in the place where they should be.

Partial stack trace:
04-May-2016 14:52:51.508 SEVERE [http-nio-8084-exec-12] com.sun.faces.context.AjaxExceptionHandlerImpl.handlePartialResponseError java.lang.ArrayIndexOutOfBoundsException: -1
at java.util.concurrent.CopyOnWriteArrayList.get(CopyOnWriteArrayList.java:368)
at java.util.concurrent.CopyOnWriteArrayList.get(CopyOnWriteArrayList.java:377)
at PlanNodeImpl.getChildAt(PlanNodeImpl.java:74)
at org.icefaces.ace.model.tree.ListNodeDataModel.navToChild(ListNodeDataModel.java:127)
at org.icefaces.ace.model.tree.ListNodeDataModel.navToChild(ListNodeDataModel.java:24)
at org.icefaces.ace.component.tree.Tree.setNodeToChild(Tree.java:178)
at org.icefaces.ace.component.tree.Tree.iterateTreeLevel(Tree.java:880)
at org.icefaces.ace.component.tree.Tree.iterateTreeLevel(Tree.java:881)
at org.icefaces.ace.component.tree.Tree.iterateTreeLevel(Tree.java:881)
at org.icefaces.ace.component.tree.Tree.iterateTreeLevel(Tree.java:881)
at org.icefaces.ace.component.tree.Tree.iterate(Tree.java:822)
at org.icefaces.ace.component.tree.Tree.processValidators(Tree.java:348)
       ...