ExtJS: Incorrect Dropdown Menu Alignment

I've got a splitbutton with a menu and a custom menuAlign setting (so that the top-right corner of the drop-down menu will be aligned with the bottom-right corner of the splitbutton).

Problem: the first time you click the splitbutton, the menu isn't aligned correctly. Subsequent clicks work fine, however. Seeing the same behavior in Chrome and FF, ExtJS 4.0.2a.

Any ideas? Thanks!

{
    xtype: 'toolbar',
    items: [
        {
            xtype: 'triggerfield',
            width: 335,
            emptyText: 'Search',
            triggerCls: 'x-form-search-trigger'
        },
        '->',
        {
            xtype: 'splitbutton',
            text: 'Account',
            menuAlign: 'tr-br',
            menu: {
                xtype: 'menu',
                plain: true,
                items: [
                    {
                        xtype: 'container',
                        html: 'image here...'
                    },
                    {
                        xtype: 'button',
                        width: 10,
                        text: 'Log Out'
                    }
                ]
            }
        }
    ]
}