also check for visibility of the layer in the central place: the update function

lib/OpenLayers/Strategy/BBOX.js

@@ -81,20 +81,11 @@ OpenLayers.Strategy.BBOX = OpenLayers.Class(OpenLayers.Strategy, {
         if(activated) {
             this.layer.events.on({
                 "moveend": this.update,
-                scope: this
-            });
-            this.layer.events.on({
                 "refresh": this.update,
+                "visibilitychanged": this.update,
                 scope: this
             });
-            if(this.layer.visibility === true) {
+            this.update();
-                this.update();
-            } else {
-                this.layer.events.on({
-                    "visibilitychanged": this.update,
-                    scope: this
-                });
-            }
         }
         return activated;
     },
@@ -134,7 +125,7 @@ OpenLayers.Strategy.BBOX = OpenLayers.Class(OpenLayers.Strategy, {
     update: function(options) {
         var mapBounds = this.getMapBounds();
         if (mapBounds !== null && ((options && options.force) ||
-                                   (this.layer.calculateInRange() && this.invalidBounds(mapBounds)))) {
+          (this.layer.visibility && this.layer.calculateInRange() && this.invalidBounds(mapBounds)))) {
             this.calculateBounds(mapBounds);
             this.resolution = this.layer.map.getResolution(); 
             this.triggerRead(options);