Starting activity from onPostExecute(String result) doesn't set ui flags

My overall goal here is to hide the navigation bars when I start an activity in my Android app.

I have two activities, the first one is a login screen and has an async task running and depending on the out come of the result I start my new activity

OnPostExecute in first activity

 .....

 @Override
    protected void onPostExecute(String result)
    {

        try
        {
            if (result.equals("true"))
            {
                Intent intent = new Intent(mContext, MainRota.class);
                startActivity(intent);
                finish();

            }
            else
            {
                CharSequence text = "One or more fields are incorrect!";
                int duration = Toast.LENGTH_SHORT;
                Toast toast = Toast.makeText(mContext, text, duration);
                toast.show();
            }
        }
        catch (Exception e)
        {
            e.printStackTrace();
        }
    }

The second activity immediately sets the ui flags to hide the nav bars

OnCreate of second activity

.....

@Override
protected void onCreate(Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.my_layout);

    View decorView = getWindow().getDecorView();
 // Hide both the navigation bar and the status bar.
 // SYSTEM_UI_FLAG_FULLSCREEN is only available on Android 4.1 and higher, but as
 // a general rule, you should design your app to hide the status bar whenever you
// hide the navigation bar.
    int uiOptions = View.SYSTEM_UI_FLAG_LAYOUT_HIDE_NAVIGATION
                             | View.SYSTEM_UI_FLAG_FULLSCREEN
                             | View.SYSTEM_UI_FLAG_IMMERSIVE
                             | View.SYSTEM_UI_FLAG_LAYOUT_STABLE
                             | View.SYSTEM_UI_FLAG_HIDE_NAVIGATION;

    decorView.setSystemUiVisibility(uiOptions);
}

when the second activity is started it is almost as if the flags are ignored and the bars are not hidden.

If i start the second activity straight from the onCreate of the first activity it works fine, but obviously i am by passing my login doing this.

Does anyone know why this happens and how to fix as I was under the impression onPostExecute runs on the main thread so there shouldn't be a problem starting an activity here.

Update!!

I have found what is causing the issue but i am still not sure why.

From the login activity i had added a listener so that when you typed the password in and pressed "done" it logged straight in rather than having to hit the login button. If i remove this listener and go back to using the login button it works fine. here is my listener code.

((EditText)findViewById(R.id.password)).setOnEditorActionListener(
      new EditText.OnEditorActionListener() 
      {
          @Override
          public boolean onEditorAction(TextView v, int actionId, KeyEvent event)
          {
              if (actionId == EditorInfo.IME_ACTION_SEARCH ||
                          actionId == EditorInfo.IME_ACTION_DONE ||
                          event.getAction() == KeyEvent.ACTION_DOWN &&
                                  event.getKeyCode() == KeyEvent.KEYCODE_ENTER)
              {
                  new GetJSONResult().execute("");
                  return true;
              }
              return false;
          }
      });

and here is my login button

    LoginButton = (Button) findViewById(R.id.loginButton2);
    LoginButton.setOnClickListener(new View.OnClickListener()
    {
        @Override
        public void onClick(View arg0)
        {
            new GetJSONResult().execute("");
        }
    });

So the question now is, why would calling the asyncTask from the listener on the EditText cause the systemUI flags to be ignored on the new activity I start from the OnPostExecute