[4.2.x/5-beta] TreePanel + BufferedRenderer = inconsistent display + errors

Use this fiddle :

http://ift.tt/1ndpJPA

or code below.

How to reproduce :

- scroll to the bottom

- expand node #271

=> children show on node #281

- expand another node ( previous one, #268 for instance )

=> same children misplacement

- scroll up

=> console blows up

Code:

Ext.require([
    'Ext.*'
]);
 
Ext.define('TestModel', {
    extend: 'Ext.data.TreeModel',
     idProperty: 'id',
    fields: [
        {name: 'id',     type: 'int'},
        {name: 'code',     type: 'string'},
        {name: 'text',     type: 'string'}
    ]
});

Ext.onReady(function() {
    var idx = 1 ;
    
    var createThreeChildren = function(node) {
        if( node.getDepth() >= 4 ) {
            node.collapse() ;
            idx++ ;
            node.appendChild({
                id: idx,
                code: 'CODE_'+idx,
                text: 'Last expand 1',
                leaf: true
            }) ;
            idx++ ;
            node.appendChild({
                id: idx,
                code: 'CODE_'+idx,
                text: 'Last expand 2',
                leaf: true
            }) ;
            return ;
        }
        var childNode ;
        for( var i=0 ; i<3 ; i++ ) {
            idx++ ;
            childNode = node.appendChild({
                id: idx,
                code: 'CODE_'+idx,
                text: 'Text '+idx,
                children: [],
                expanded: true
            }) ;
            createThreeChildren(childNode) ;
        }
    } ;
    
    var treestore = Ext.create('Ext.data.TreeStore',{
        model: 'TestModel',
        root: {
            id: 1,
            code: 'ROOT',
            text: 'Root',
            expanded: true,
            children: []
        },
        proxy: {
            type: 'memory' ,
            reader: {
                type: 'json'
            }
        }
    }) ;
    
    var treeroot = treestore.getRootNode() ;
    createThreeChildren(treeroot) ;
    
    Ext.create('Ext.tree.Panel',{
        width: 500,
        height: 600,
        renderTo: Ext.getBody(),
        animate: false,
        useArrows: true,
        rootVisible: true,
        store: treestore,
        plugins: [{
            ptype: 'bufferedrenderer'
        }],
        columns: [{
            xtype: 'treecolumn', //this is so we know which column will show the tree
            text: 'Code',
            width: 200,
            dataIndex: 'code'
        },{
            text: 'Text',
            width: 200,
            dataIndex: 'text'
        }],
    }) ;
}) ;