The default "thumb" resources for the Slider are not properly resolving in a portlet. If we assume we have the Slider on a portal page with the following URL:

http://localhost:8080/web/guest/ace-maint

there are are a couple of "thumb-*" images that are being rendered out. Firebug shows 404 not found for:

http://localhost:8080/web/guest/javax.faces.resource/assets/skins/sam/thumb-x.png.jsf?ln=yui/3_1_1
http://localhost:8080/web/guest/javax.faces.resource/assets/skins/sam/thumb-y.png.jsf?ln=yui/3_1_1

These URLs are missing information about the portlet namespace and other Liferay attributes. I can manually get it to resolve in the browser by taking a copy of a resource that is resolving and simply massaging it into a working one like so:

http://localhost:8080/web/guest/ace-maint?_slider_WAR_aceshowcaseportlet_INSTANCE_R8mz_javax.faces.resource=assets/skins/sam/thumb-x.png&_slider_WAR_aceshowcaseportlet_INSTANCE_R8mz_ln=yui%2F3_1_1&p_p_cacheability=cacheLevelPage&p_p_col_count=1&p_p_col_id=column-1&p_p_id=slider_WAR_aceshowcaseportlet_INSTANCE_R8mz&p_p_lifecycle=2&p_p_mode=view&p_p_state=normal

Looking at the SliderEntry.java class, we have the following code:

    public String getThumbUrl() {
     String thumbUrl = super.getThumbUrl();
     if (null == thumbUrl) {
     if ("x".equals(getAxis())) {
     thumbUrl = "javax.faces.resource/assets/skins/sam/thumb-x.png.jsf?ln=yui/3_3_0";
     } else {
     thumbUrl = "javax.faces.resource/assets/skins/sam/thumb-y.png.jsf?ln=yui/3_3_0";
     }
     }
     return thumbUrl;
    }

It's not possible to simply hard code in URL references like this and have them successfully resolve. For portlets, this will miss portal specific attributes as well as the namespacing. This is particulary true in portlets but it could be relevant in a stock servlet application as well.