Api dealing with outdated RequestQueue

The issue
If we search once or more, then click back, navigate to the app again, and try to search again, no callback methods get called.

why?
If we click back from the activity the API object still the same because it's a static object
and if we navigate again to the activity, we are creating a new RequestQueue in the onCreate() of the FlickrSearchActivity, but in Api.get(requestQueue) the API object is not null so here we are dealing with two request queues and the callback functions is never called.