diff --git a/src/main/scala/com/github/shadowsocks/BaseService.scala b/src/main/scala/com/github/shadowsocks/BaseService.scala
index 67ea792d..701ca73f 100644
--- a/src/main/scala/com/github/shadowsocks/BaseService.scala
+++ b/src/main/scala/com/github/shadowsocks/BaseService.scala
@@ -56,6 +56,7 @@ trait BaseService extends Service {
   var trafficMonitorThread: TrafficMonitorThread = null
 
   final val callbacks = new RemoteCallbackList[IShadowsocksServiceCallback]
+  var callbacksCount: Int = _
 
   val binder = new IShadowsocksService.Stub {
     override def getMode: Int = {
@@ -67,19 +68,19 @@ trait BaseService extends Service {
     }
 
     override def unregisterCallback(cb: IShadowsocksServiceCallback) {
-      if (cb != null ) {
-        callbacks.unregister(cb)
-      }
-      if (callbacks.getRegisteredCallbackCount == 0 && timer != null) {
-        timer.cancel()
-        timer = null
+      if (cb != null && callbacks.unregister(cb)) {
+        callbacksCount -= 1
+        if (callbacksCount == 0 && timer != null) {
+          timer.cancel()
+          timer = null
+        }
       }
     }
 
     override def registerCallback(cb: IShadowsocksServiceCallback) {
-      if (cb != null) {
-        callbacks.register(cb)
-        if (callbacks.getRegisteredCallbackCount != 0 && timer == null) {
+      if (cb != null && callbacks.register(cb)) {
+        callbacksCount += 1
+        if (callbacksCount != 0 && timer == null) {
           val task = new TimerTask {
             def run {
               if (TrafficMonitor.updateRate()) updateTrafficRate()
@@ -160,7 +161,7 @@ trait BaseService extends Service {
   def updateTrafficRate() {
     val handler = new Handler(getContext.getMainLooper)
     handler.post(() => {
-      if (callbacks.getRegisteredCallbackCount > 0) {
+      if (callbacksCount > 0) {
         val txRate = TrafficMonitor.getTxRate
         val rxRate = TrafficMonitor.getRxRate
         val txTotal = TrafficMonitor.getTxTotal
@@ -181,7 +182,7 @@ trait BaseService extends Service {
   protected def changeState(s: Int, msg: String) {
     val handler = new Handler(getContext.getMainLooper)
     handler.post(() => if (state != s) {
-      if (callbacks.getRegisteredCallbackCount > 0) {
+      if (callbacksCount > 0) {
         val n = callbacks.beginBroadcast()
         for (i <- 0 until n) {
           try {
diff --git a/src/main/scala/com/github/shadowsocks/Shadowsocks.scala b/src/main/scala/com/github/shadowsocks/Shadowsocks.scala
index 2f949e41..82d1b04c 100644
--- a/src/main/scala/com/github/shadowsocks/Shadowsocks.scala
+++ b/src/main/scala/com/github/shadowsocks/Shadowsocks.scala
@@ -104,7 +104,6 @@ class Shadowsocks
   var progressDialog: ProgressDialog = _
   var progressTag = -1
   var state = State.STOPPED
-  var prepared = false
   var currentProfile = new Profile
   var vpnEnabled = -1
   var trafficCache: String = _
@@ -402,7 +401,6 @@ class Shadowsocks
   protected override def onPause() {
     super.onPause()
     ShadowsocksApplication.profileManager.save
-    prepared = false
   }
 
   private def stateUpdate() {
@@ -517,7 +515,6 @@ class Shadowsocks
 
   override def onActivityResult(requestCode: Int, resultCode: Int, data: Intent) = resultCode match {
     case Activity.RESULT_OK =>
-      prepared = true
       serviceStart()
     case _ =>
       cancelStart()
diff --git a/src/main/scala/com/github/shadowsocks/ShadowsocksSettings.scala b/src/main/scala/com/github/shadowsocks/ShadowsocksSettings.scala
index 21318675..25a39f88 100644
--- a/src/main/scala/com/github/shadowsocks/ShadowsocksSettings.scala
+++ b/src/main/scala/com/github/shadowsocks/ShadowsocksSettings.scala
@@ -166,18 +166,16 @@ class ShadowsocksSettings extends PreferenceFragment with OnSharedPreferenceChan
     isProxyApps.setChecked(ShadowsocksApplication.settings.getBoolean(Key.isProxyApps, false))  // update
   }
 
-  override def onPause {
-    super.onPause()
+  override def onDestroy {
+    super.onDestroy()
     ShadowsocksApplication.settings.unregisterOnSharedPreferenceChangeListener(this)
   }
 
   def onSharedPreferenceChanged(sharedPreferences: SharedPreferences, key: String) = key match {
-    case Key.isNAT =>
-      activity.handler.post(() => {
-        activity.deattachService
-        activity.attachService
-      })
-      setEnabled(enabled)
+    case Key.isNAT => activity.handler.post(() => {
+      activity.deattachService
+      activity.attachService
+    })
     case _ =>
   }
 
diff --git a/src/main/scala/com/github/shadowsocks/database/DBHelper.scala b/src/main/scala/com/github/shadowsocks/database/DBHelper.scala
index e29c8548..7d6d5dbc 100644
--- a/src/main/scala/com/github/shadowsocks/database/DBHelper.scala
+++ b/src/main/scala/com/github/shadowsocks/database/DBHelper.scala
@@ -105,17 +105,14 @@ class DBHelper(val context: Context)
           " ipv6, individual FROM `tmp`;")
         profileDao.executeRawNoArgs("DROP TABLE `tmp`;")
         profileDao.executeRawNoArgs("COMMIT;")
-        return
-      }
-
-      if (oldVersion < 13) {
+      } else if (oldVersion < 13) {
         profileDao.executeRawNoArgs("ALTER TABLE `profile` ADD COLUMN tx LONG;")
         profileDao.executeRawNoArgs("ALTER TABLE `profile` ADD COLUMN rx LONG;")
         profileDao.executeRawNoArgs("ALTER TABLE `profile` ADD COLUMN date VARCHAR;")
       }
 
       if (oldVersion < 15) {
-        profileDao.executeRawNoArgs("ALTER TABLE `profile` ADD COLUMN userOrder LONG;")
+        if (oldVersion >= 12) profileDao.executeRawNoArgs("ALTER TABLE `profile` ADD COLUMN userOrder LONG;")
         var i = 0
         for (profile <- profileDao.queryForAll.asScala) {
           if (oldVersion < 14) profile.individual = updateProxiedApps(context, profile.individual)