title: having multiple ajax responses for one request
body: <p>I have some problems with ajax responses. Everything is working okay, however I got some strange behaviours.
  I am making an ajax-based chat. So, I use ajax requests-responses to make the stuff work. It is working fine, albeit since I started to use 2 polling functions sometimes the responses are retrieved multiple times.
  In specifics: I send 1 ajax package for message polling, and 1 ajax package for userlist polling. Both of them are sent periodically! Furthermore, they are sent with same frequency in about same time.
  Sometimes they have a problem: for a request multiple responses are sent back. All packages have a timestamp and they are logged on the server-side. On the server the package only got in once (I am sure based on logging, and using multiple browsers at the same time). The browser makes the response about 3-4 times. All messages are completely same, with the same timestamp. This usually happens when there is a heavy load on the browser.
  I tried to disable cache in the header but it does not help too.
  Please help with any information or idea about the problem.</p>