Incorrect display of Blue Marble

Hello all,
I have set up a Nasa OnEarth Box instance and am trying to serve a WMS service to a sandbox. My code is as follows:

var viewer = new Cesium.Viewer('cesiumContainer',{
    baseLayerPicker : false,
    imageryProvider: new Cesium.WebMapServiceImageryProvider({
        url: "http://localhost:8080/onearth/demo/mapserver/mapserver.cgi?SERVICE=WMS" +
        "&VERSION=1.3.0&REQUEST=GetMap&FORMAT=image%2Fjpeg&TRANSPARENT=true&" +
        "&bbox={westProjected}%2C{southProjected}%2C{eastProjected}%2C{northProjected}&" +
        layers : 'blue_marble',
        proxy: new Cesium.DefaultProxy('/proxy/')

The default configuration is a Geographic coordinate system. The service is set up to deliver EPSG 4326 imagery (Geographic). The tiles delivered are correct until the halfway point in each direction.

You can see the error:

What can I do to correct this ordering? What could be wrong? Has anyone seen this before?