Android GCM registration / device id for push notification changes every time

I used this code to get the gcm registration id. ( Formerly )

// Make sure the device has the proper dependencies.
        GCMRegistrar.checkDevice(this);

        // Make sure the manifest was properly set - comment out this line
        // while developing the app, then uncomment it when it ready.
        GCMRegistrar.checkManifest(this);



//        registerReceiver(mHandleMessageReceiver, new IntentFilter(
//                CommonUtilities.DISPLAY_MESSAGE_ACTION));

        // Get GCM registration id
        final String regId = GCMRegistrar.getRegistrationId(this);

        // Check if regid already presents
        if (regId.equals("")) {
            // Registration is not present, register now with GCM           
            GCMRegistrar.register(this, CommonUtilities.SENDER_ID);


        } else {

            AppSharedPreferences.saveDeviceIDPreference(ctx, regId);

            // Device is already registered on GCM
            if (GCMRegistrar.isRegisteredOnServer(this)) {
                // Skips registration.              



//                Toast.makeText(getApplicationContext(), "Already registered with GCM", Toast.LENGTH_LONG).show();
            } else {
                // Try to register again, but not in the UI thread.
                // It also necessary to cancel the thread onDestroy(),
                // hence the use of AsyncTask instead of a raw thread.
                final Context context = this;
                mRegisterTask = new AsyncTask<Void, Void, Void>() {

                    @Override
                    protected Void doInBackground(Void... params) {
                        // Register on our server
                        // On server creates a new user
                        ServerUtilities.register(context, regId);
                        return null;
                    }

                    @Override
                    protected void onPostExecute(Void result) {
                        mRegisterTask = null;
                    }

                };
                mRegisterTask.execute(null, null, null);
            }
        }

      

        
        
        
      

    

But, shockingly, he seems to change each time the performance, . Please let me know the possible reason for this. for the same device and same application

EDITED

modified GCM to newer version

gcm = GoogleCloudMessaging.getInstance(this);
new RegisterBackground().execute();

      

        
        
        
      

    

Further on this tutorial .

But, still the same behavior, that is, getting a new reg id with each installation.