vtswingkid, thanks for pointing that out. In fact, I've also made the same adjustment to the getGroupValue method as well. Here are the updated methods:
    getGroupValue : function(){
    	var p = this.el.up('form') || Ext.getBody();
        return p.child('input[name='+this.el.dom.name+']:checked', true).value;
    // private
    onClick : function(){
    	if(this.el.dom.checked != this.checked){
    		var p = this.el.up('form') || Ext.getBody();
			var els = p.select('input[name='+this.el.dom.name+']');
				if(el.dom.id == this.id){
			}, this);
I've committed this fix to SVN for both 1.1 and 2.0 (1.1 uses Ext.get(document.body) instead of Ext.getBody()).

BTW, the RadioGroup ux looks pretty good so far. We'll probably consider doing something similar in a future release, but for now that should work great for people.