incorporate suggestions by @ahocevar and @elemoine

Author: Bart van den Eijnden

lib/OpenLayers/Layer.js

@@ -86,13 +86,13 @@ OpenLayers.Layer = OpenLayers.Class({
      * element - {DOMElement} A reference to layer.events.element.
      *
      * Supported map event types:
-     * loadstart - Triggered when layer loading starts. When using Fixed or
-     *     BBOX strategies, the event object includes a *filter* property
-     *     holding the OpenLayers.Filter used when calling read on the 
-     *     protocol.
-     * loadend - Triggered when layer loading ends.  When using Fixed or BBOX
-     *     strategies, the event object includes a *response* property holding
-     *     an OpenLayers.Protocol.Response object.
+     * loadstart - Triggered when layer loading starts.  When using a Vector 
+     *     layer with a Fixed or BBOX strategy, the event object includes 
+     *     a *filter* property holding the OpenLayers.Filter used when 
+     *     calling read on the protocol.
+     * loadend - Triggered when layer loading ends.  When using a Vector layer
+     *     with a Fixed or BBOX strategy, the event object includes a 
+     *     *response* property holding an OpenLayers.Protocol.Response object.
      * visibilitychanged - Triggered when layer visibility is changed.
      * move - Triggered when layer moves (triggered with every mousemove
      *     during a drag).

lib/OpenLayers/Strategy/BBOX.js

@@ -217,11 +217,11 @@ OpenLayers.Strategy.BBOX = OpenLayers.Class(OpenLayers.Strategy, {
             this.layer.protocol.abort(this.response);
             this.layer.events.triggerEvent("loadend");
         }
-        var filter = this.createFilter();
-        this.layer.events.triggerEvent("loadstart", {filter: filter});
+        var evt = {filter: this.createFilter()};
+        this.layer.events.triggerEvent("loadstart", evt);
         this.response = this.layer.protocol.read(
             OpenLayers.Util.applyDefaults({
-                filter: filter,
+                filter: evt.filter,
                 callback: this.merge,
                 scope: this
         }, options));