Stock Lightbox doesn't show the Prev option if it's the first image. Likewise stock doesn't show the Next option if it's the last. I think it should just jump to the start or the end and it's really simple to do:

Code:
......
        initEvents: function() {
            var close = function(ev) {
                ev.preventDefault();
                this.close();
            };

            els.overlay.on('click', close, this);
            els.loadingLink.on('click', close, this);
            els.navClose.on('click', close, this);

            els.lightbox.on('click', function(ev) {
                if(ev.getTarget().id == 'ux-lightbox') {
                    this.close();
                }
            }, this);

            els.navPrev.on('click', function(ev) {
                ev.preventDefault();
                this.setImage(activeImage - 1);
            }, this);

            els.navNext.on('click', function(ev) {
                ev.preventDefault();
                if (activeImage === (images.length - 1)) {
                    var goTo = 0;
                } else {
                    var goTo = activeImage+1;
                }
                this.setImage(goTo);
            }, this);
        },
......
        updateNav: function(){
            this.enableKeyNav();

            els.hoverNav.show();
            //no if then, just show
            els.navPrev.show();
            els.navNext.show();
        },
Nothing ground breaking, just a thought to enable it.