IE 8 and client-side caching - asp.net

Question

Background story:
I have a web portal in .NET 3.5 on an IIS 6 web server. Currently there is a page that is given a value and based on that value looks up a PDF file on a web service and displays the results to the user in another tab in the web page. This is done with the following code.
context.Response.ClearContent();
context.Response.ClearHeaders();
context.Response.Clear();
context.Response.AddHeader("Accept-Header", pdfStream.Length.ToString());
context.Response.ContentType = "application/pdf";
context.Response.BinaryWrite(pdfStream.ToArray());
context.Response.Flush();
This works and has worked for years. However we got an issue from the client that a particular client was having the PDF returned as the same PDF every time until they cleared temp internet cache.
I thought oh cool, this is an easy one. I will just add the cache headers to the response to never cache it. So I added the following:
context.Response.Cache.SetCacheability(HttpCacheability.NoCache);//IE set to not cache
context.Response.Cache.SetNoStore();//Firefox/Chrome not to cache
context.Response.Cache.SetExpires(DateTime.UtcNow); //for safe measure expire it immediately
After a quick test I got exactly what I was expecting in the response header.
Cache-Control no-cache, no-store
Pragma no-cache
Expires -1
The Problem:
So this went live. Everything seemed cool day one. The day after, bam, everyone started getting white screens and no PDF displayed. After further investigation, I found out it was only IE 6,7,8. Chrome is fine, Firefox fine, safari fine, even IE 9 fine. Without knowing the why this happened, I reverted my change and deployed it, and everything started worked again.
I have searched all over trying to find out why my caching headers seemed to confuse IE 6-8 to no avail. Has anyone experienced this type of issue with IE 6-8? Is there something I am missing? Thanks for any insight.

Answer 1

I found the solution. Here is what tipped me off. Here is a link
Basically IE8 (and lower) was having issues with the Cache-Control header if it had no-cache or store-cache. I was able to work around the problem by basically allowing private caching only and set a max age to very short so it expires almost immediately.
//Ie 8 and lower have an issue with the "Cache-Control no-cache" and "Cache-Control store-cache" headers.
//The work around is allowing private caching only but immediately expire it.
if ((Request.Browser.Browser.ToLower() == "ie") && (Request.Browser.MajorVersion < 9))
{
context.Response.Cache.SetCacheability(HttpCacheability.Private);
context.Response.Cache.SetMaxAge(TimeSpan.FromMilliseconds(1));
}
else
{
context.Response.Cache.SetCacheability(HttpCacheability.NoCache);//IE set to not cache
context.Response.Cache.SetNoStore();//Firefox/Chrome not to cache
context.Response.Cache.SetExpires(DateTime.UtcNow); //for safe measure expire it immediately
}