Fixed race condition.

app/assets/javascripts/app/controllers/maintenance.coffee

@@ -37,13 +37,19 @@ class Index extends App.ControllerContent
   setMode: (e) =>
     value = @modeSetting.prop('checked')
     callback = ->
-      App.Setting.set('maintenance_mode', value)
+      App.Setting.set(
+        'maintenance_mode',
+        value,
+        {
+          done: ->
             App.WebSocket.send(
               event:'maintenance'
               data:
                 type: 'mode'
                 on: value
             )
+        }
+      )
     if value
       new App.ControllerConfirm(
         message: 'Sure?'