diff --git a/panel.js b/panel.js
index 13b4cc2..a532081 100644
--- a/panel.js
+++ b/panel.js
@@ -881,6 +881,7 @@ var dtpPanel = Utils.defineClass({
                         this._disconnectVisibleId(actor);
                         this._refreshVerticalAlloc();
                     });
+                    actor.connect('destroy', () => actor._dtpVisibleId = 0);
                 }
 
                 if (child) {
@@ -903,9 +904,10 @@ var dtpPanel = Utils.defineClass({
     _disconnectVisibleId: function(actor) {
         if (actor._dtpVisibleId) {
             actor.disconnect(actor._dtpVisibleId);
-            delete actor._dtpVisibleId;
-            this._unmappedButtons.splice(this._unmappedButtons.indexOf(actor), 1);
         }
+
+        delete actor._dtpVisibleId;
+        this._unmappedButtons.splice(this._unmappedButtons.indexOf(actor), 1);
     },
 
     _setActivitiesButtonVisible: function(isVisible) {