--- xfce4-panel-4.12.0.orig/plugins/tasklist/tasklist-widget.c	2015-02-26 21:32:17.000000000 +0100
+++ xfce4-panel-4.12.0/plugins/tasklist/tasklist-widget.c	2015-06-23 12:01:47.935828987 +0200
@@ -334,6 +334,7 @@
 static void               xfce_tasklist_group_button_add_window          (XfceTasklistChild    *group_child,
                                                                           XfceTasklistChild    *window_child);
 static XfceTasklistChild *xfce_tasklist_group_button_new                 (WnckClassGroup       *class_group,
+                                                                          guint                unique_id,
                                                                           XfceTasklist         *tasklist);
 
 /* potential public functions */
@@ -1683,7 +1684,7 @@
           if (group_child == NULL)
             {
               /* create group button for this window and add it */
-              group_child = xfce_tasklist_group_button_new (child->class_group, tasklist);
+              group_child = xfce_tasklist_group_button_new (child->class_group, child->unique_id, tasklist);
               g_hash_table_insert (tasklist->class_groups,
                                    g_object_ref (child->class_group),
                                    group_child);
@@ -3104,14 +3105,17 @@
                           XfceTasklist *tasklist)
 {
   XfceTasklistChild *child;
-  static guint       unique_id_counter = 0;
+  /* The buttons with unique_id equal 0 are the wrong buttons. Start unique_id_counter from 1.
+     This is besser for debugging.
+  */
+  static guint       unique_id_counter = 1;
 
   panel_return_val_if_fail (XFCE_IS_TASKLIST (tasklist), NULL);
   panel_return_val_if_fail (WNCK_IS_WINDOW (window), NULL);
 
   /* avoid integer overflows */
   if (G_UNLIKELY (unique_id_counter >= G_MAXUINT))
-    unique_id_counter = 0;
+    unique_id_counter = 1;
 
   child = xfce_tasklist_child_new (tasklist);
   child->type = CHILD_TYPE_WINDOW;
@@ -3668,9 +3672,9 @@
 }
 
 
-
 static XfceTasklistChild *
 xfce_tasklist_group_button_new (WnckClassGroup *class_group,
+                                guint           unique_id,
                                 XfceTasklist   *tasklist)
 {
   XfceTasklistChild *child;
@@ -3681,6 +3685,7 @@
   child = xfce_tasklist_child_new (tasklist);
   child->type = CHILD_TYPE_GROUP;
   child->class_group = class_group;
+  child->unique_id = unique_id;
 
   /* note that the same signals should be in the proxy menu item too */
   g_signal_connect (G_OBJECT (child->button), "button-press-event",