Async WCF calls with impersonation

I was playing around with impersonated asynchronous WCF calls and discovered a strange behaviour on the WCF server side: most of the time the identity was the correct impersonated identity but sometimes it was only the client process identity (like 'hostname$'). I was looking at all different configuartion hells of WCF but did not find any solution to fix the problem.

After searching the web I found two interesting posts from Micorosft:

http://msdn.microsoft.com/en-us/library/aa738624.aspx

and

http://support.microsoft.com/?scid=kb%3Ben-us%3B976123&x=10&y=14

The first document stated that I am trying to use an unsupported scenario. The second document says that there is a hotfix available for Vista and Windows Server 2008 (SP2 and higher).

Unfortunately my customer is running Windows 2003 SP2. So there seems to be no way to use async WCF calls with impersonation. Very sad.