Issue Sending multiple requests using BaseProxy

I have UI modules that fire multiple requests using the a subclass of BaseProxy. Everything works fine as long as I fire a single request at a time and wait for it to return. If I fire two requests one after the other (being asynchronous), I do not get a response at all. Is the BaseProxy limited to just one request at a time or am I missing something. I use a new instance of BaseProxy for each request.

Thanks,