According to OpenLayers API, the AnchoredBubble() function is deprecated:

/**
 * Class: OpenLayers.Popup.AnchoredBubble
 * This class is *deprecated*. Use {<OpenLayers.Popup.Anchored>} and
 * round corners using CSS3's border-radius property.
 * 
 * Inherits from: 
 *  - <OpenLayers.Popup.Anchored>
 */

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