jQuery Async Call only "parallel" when URL's different

I was playing with jQuery and async calls last night and found an unusual issue. I wanted to run multiple Ajax calls inside a loop. I wrote the below (where rand.php just sleeps for a second and returns a random number). Somewhat surprisingly it executes synchronously and takes 20 seconds or so to finish.

$(document).ready(function () {
    $([1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20]).each(function() {
        var number = this;

        $.get("rand.php", function(data) {
            $('#'+number).html(data);
        });
    });
});

The PHP code is as follows,

<?php
sleep(1);
echo rand(); 
?>

I was thinking this is clearly wrong as the async calls should be no blocking and return almost in parallel. After much playing around (assuming it was a server issue) I discovered that appending anything to the URL to make it look like it was different worked as expected. That is it returned in 3 seconds or so (6 or so calls at a time).

$(document).ready(function () {
    $([1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20]).each(function() {
        var number = this;

        $.get("rand.php?"+number, function(data) {
            $('#'+number).html(data);
        });
    });
});

I don't suppose a jQuery/Javascript Guru can explain this behavior? Is it some browser limitation? Why is it that only when the URL's are different that it runs as I would expect?

EDIT - Rather then reply, this was using Chrome (whatever the latest is) and Firefox 5/6. I did try it in IE which did cache it, so ignored that and focused on开发者_Python百科 Chrome. Interesting the first one works as expected in IE9 on the first page load, but then just displays cached results when reloaded.

---

You are in ie aren't you. Bad! Bad IE user! IE caches get requests as if it was any other content. Jquery has a built in function to address this:

$.ajaxSetup({ cache : false });

This will add a nifty spoiler to take care of this. But why add the spoiler in other browsers? So usually I do this:

if(!+"\v1"){
    $.ajaxSetup({ cache : false });
}

Which is the tests for IE and set it only in that browser.