Index: user.rb
===================================================================
--- user.rb	(revision 17403)
+++ user.rb	(working copy)
@@ -445,7 +445,12 @@
     if Setting.session_timeout?
       scope = scope.where("updated_on > ?", Setting.session_timeout.to_i.minutes.ago)
     end
-    scope.update_all(:updated_on => Time.now) == 1
+    last_updated = scope.maximum(:updated_on)
+    if last_updated.nil? || last_updated <= 1.minute.ago
+      scope.update_all(:updated_on => Time.now) == 1
+    else
+      true
+    end
   end
 
   # Return an array of project ids for which the user has explicitly turned mail notifications on