Buttons add the focus class to the *outermost element*, not the focusEl!
function(e) {
        var me = this;

        // Set this flag, so that when AbstractComponent's onFocus gets the focusEl to add the focusCls
        // to, it will get the encapsulating element - that's what the CSS rules for Button need right now
        me.useElForFocus = true;
        me.callParent(arguments);
        me.useElForFocus = false;
    }