When .show() is called on an element which has 'visibility: hidden', it simply ignores this. I'd say .show() is a way to simply tell the element to show itself! So therefore I suggest the following solution to make .show() also work on invisible elements;

	show: function(speed,callback){
		return speed ?
			this.animate({
				height: "show", width: "show", opacity: "show"
			}, speed, callback) :
			
			this.filter(":hidden").each(function(){
				this.style.display = this.oldblock ? this.oldblock : "";
				if ( jQuery.css(this,"display") == "none" )
					this.style.display = "block";
				if ( jQuery.css(this,"visibility") == "hidden" )
					this.style.visibility = "visible";
			}).end();
	},