GeoServer - Single Image Request - Graphic Label Issues

I posted this on the OSGEO GeoServer Mailing List but received no love, so I'll try here.

I have GS 2.6.0. connected to a PostgreSQL 9.2 DB (PostGIS 2.1). I have an SLD where I am trying use graphic label options to label a bunch of weather conditions throughout 700 cities. I like how GS does not allow labels to conflict, but things are not working well. When I first open my OpenLayers 3 Map, the graphic label (icons) show nicely:

All the tiny black dots are cities I am try to overlay weather conditions. As I zoom in, I would expect different areas to be labeled, and when I zoom in ONE level, the graphics are still there.

But, when I zoom in one more level, and all subsequent levels, all the graphic labels disappear:

I am using OpenLayers 3.0 and am requesting a single image like this:

var openWeatherMap = new ol.layer.Image({ 
    visible: false, 
    refresh: true, 
    extent: mapExtent, 
    source: new ol.source.ImageWMS({ 
            'crossOrigin':'anonymous', 
            url: 'http://ift.tt/1E0dyBP', 
            params: {'LAYERS': 'feed_open_weather_map'}, 
            serverType: 'geoserver' 
    })

});

I've tried a million combinations of OL3 and SLD options. Some work better than other, but I can't ever get the graphic labels to appear beyond the zoom I mentioned. My SLD looks like this: SLD Sorry for the pastebin. Does anyone know why GeoServer is not labeling with graphic properly?

Update: added getMap request samples. The getMap request that shows the graphic labels is:

http://ift.tt/1HM7ONp

When I put this in the browser, it shows the graphic labels.

The getMap request that does not show the graphic labels is:

http://ift.tt/1NjCi7H

When I put this in the browser, I only get the features (tiny dots) but no graphic labels: