fix duplicate column

newsbox/admin.py

@@ -394,11 +394,12 @@ class NewsboxExpiredAdmin(NewsboxBaseAdmin):
 
     def get_list_display(self, request):
         list_display = copy.copy(super(NewsboxExpiredAdmin, self).get_list_display(request))
-        try:
-            index = list_display.index('newsbox_date_short')
-            list_display[index] = 'newsbox_publication_dates_short'
-        except ValueError:
-            list_display.append('newsbox_publication_dates_short')
+        if 'newsbox_publication_dates_short' not in list_display:
+            try:
+                index = list_display.index('newsbox_date_short')
+                list_display[index] = 'newsbox_publication_dates_short'
+            except ValueError:
+                list_display.append('newsbox_publication_dates_short')
         return list_display