Why does IE8 return cached result for consecutive identical XDomainRequest messages?

Question

In my application I needed to make periodic cross-domain HTTP POST requests to receive up-to-date data from a server (periodic polling). The application was not working in IE8 while it was in Chrome. So I decided to debug this with Wireshark:

I executed 2 equivalent codes in IE8 and Chrome. I monitored my network with Wireshark. The wireshark filter is:

http.request.full_uri == "http://www.andlabs.net/html5/uCOR.php"   

I noticed that IE8 only sends the request once and returns the same cached response for the following invocations. Chrome, on the other hand, sends a new request each time.

The code I used for IE8:

var cor = new XDomainRequest();
cor.onload = function() { alert(cor.responseText);}
cor.open('POST', 'http://www.andlabs.net/html5/uCOR.php');
cor.send();

The code I used for Chrome:

var cor = new XMLHttpRequest();
cor.onload = function() { alert(cor.responseText);}
cor.open('POST', 'http://www.andlabs.net/html5/uCOR.php');
cor.send();

In order to prevent cached response in IE8 I tried the following code and it worked:

var cor = new XDomainRequest();
cor.onload = function() { alert(cor.responseText);}
cor.open('POST', 'http://www.andlabs.net/html5/uCOR.php');
cor.send(''+new Date());

Why does IE8 behave this way and is there any way to solve this in a different way than what I did? Notice that I cannot use the same trick for GET requests.

By the way the request and the response for IE are as follows:

request:

POST /html5/uCOR.php HTTP/1.1
Accept: */*
Origin: http://jsbin.com
Accept-Language: en-US
Accept-Encoding: gzip, deflate
User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.1; WOW64; Trident/4.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; Media Center PC 6.0; .NET4.0C)
Host: www.andlabs.net
Content-Length: 0
Connection: Keep-Alive
Cache-Control: no-cache

response:

HTTP/1.1 200 OK
Content-Type: text/html
Server: Microsoft-IIS/7.0
Access-Control-Allow-Origin: *
X-Powered-By: ASP.NET
Date: Tue, 17 Jan 2012 21:41:39 GMT
Content-Length: 180

This is a page from www.andlabs.net which is accessible from any website through Cross Origin Requests<br>This page contains the following header:<br>Access-Control-Allow-Origin: *

Answer 1

It looks like there aren't any caching headers on the response, so browsers may behave differently. Can you add the following header to the response: Cache-Control: no-cache