Code:



    onProxyLoad: function(operation) {
        var me = this,
            options = operation.initialConfig,
            successful = operation.wasSuccessful(),
            records = operation.getRecords(),
            node = options.node,
            scope = operation.getScope() || me,
            args = [records, operation, successful];


        if (me.isDestroyed) {
            return;
        }


        me.loading = false;
        node.set('loading', false);
        if (successful) {
            if (!me.clearOnLoad) {
                records = me.cleanRecords(node, records);
            }
            records = me.fillNode(node, records);
        }
        // The load event has an extra node parameter
        // (differing from the load event described in AbstractStore)
        /**
         * @event load
         * Fires whenever the store reads data from a remote data source.
         * @param {Ext.data.TreeStore} this
         * @param {Ext.data.NodeInterface} node The node that was loaded.
         * @param {Ext.data.TreeModel[]} records An array of records.
         * @param {Boolean} successful True if the operation was successful.
         */
        Ext.callback(options.onChildNodesAvailable, scope, args);
        me.fireEvent('load', me, operation.node, records, successful);
    },

Should pass node, not operation.node