I think this is a user agent string passed to the site. It incorrectly identifies it as IE8, as it may not meet the requirements in its logic to conform to IE9. I see the same thing happening with my box. You can specify the user agent string to use if you want. Add this to your project.
In your usage operations add ...
using System.Runtime.InteropServices;
In your form class add ....
[DllImport("urlmon.dll", CharSet = CharSet.Ansi)]
private static extern int UrlMkSetSessionOption(int dwOption, string pBuffer, int dwBufferLength, int dwReserved);
const int URLMON_OPTION_USERAGENT = 0x10000001;
public void ChangeUserAgent(String Agent)
{
UrlMkSetSessionOption(URLMON_OPTION_USERAGENT, Agent, Agent.Length, 0);
}
Then just name it somewhere in your code ... perhaps a constructor or form_load event.
ChangeUserAgent("Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; WOW64; Trident/5.0)");