ExtJS 4.1.1a override to clone all combo stores by default http://stackoverflow.com/questions/12620424/extjs-4-cloning-stores http://stackoverflow.com/questions/10714876/how-can-i-create-two-combobox-from-one-store-in-extjs

ext-clone-stores.js

Ext.override(Ext.data.Store, {
    constructor: function(config) {
        this.initConfig(config);
        this.callParent(arguments);
        this.addEvents(
            /**
             * @event clone
             * Fires when a store is cloned
             * @param {Ext.data.Store} this
             * @param {Ext.data.Store} clone The new clone
             */
            'clone'
        );
    },

    /**
     * @param preserveLocalCache Preserve local cache of records
     * @param cloneRecords If preserveLocalCache is true, also clone local cache of records
     * @return {Ext.data.Store}
     */
    clone: function(preserveLocalCache, cloneRecords) {
        var localCache = this.snapshot || this.data,
            config = this.getInitialConfig(),
            clone,
            records = [];

        if (preserveLocalCache) {
            if (cloneRecords) {
                localCache.each(function(record) {
                    records.push(record.copy());
                });
                config.data = records;
            } else {
                config.data = localCache.items;
            }
        }

        clone = new this.self(config);

        this.fireEvent('clone', this, clone);

        return clone;
    }
});
Ext.override(Ext.form.field.ComboBox, {
    /**
     * @cfg {Boolean} cloneStore
     * Whether to clone the store instance passed in the config
     */
    cloneStore: false,

    initComponent: function() {
        var store = this.store,
            preserveLocalCache = this.queryMode == 'local';

        if (Ext.isString(store)) {
            store = Ext.data.StoreManager.get(store);
        }

        if (this.cloneStore && store instanceof Ext.data.Store) {
            this.store = store.clone(preserveLocalCache);
        }

        this.callParent();
    }
});

Useful! Good job. :_)