Depending on browser settings you might run into problems with caching when calling pages through AJAX. I've run into issues with WebKit based browsers (Chrome, Safari) as it seems they are more aggressive with their caching than Firefox and even IE. This was one of the few times where something worked in IE and not Safari.

If your ajax is calling a dynamically generated page where its content changes over time you need to disable caching on the AJAX call.

In JQuery you can just set the cache parameter to false:

$.ajax({
  url: "/path/to/page/",
  type: "POST",
  cache: false,
  success: function(data){
    ...
  }
});

Another technique that you can do is to generate a random variable on each call to the end of URL to trick the browser.

$.ajax({
  url: "/path/to/page/?v=" Math.ceil(10000*Math.random()),
  type: "POST",
  success: function(data){
    ...
  }
});