You'll note that regardless of which link you click, the url in the address bar is the same as the link although both go to the same place. This indicates that you are set up for URL Framing (Framed Redirect - not the same thing as HTML Frames).
With URL Framing, as far as dns and iis are concerned, you are two separate sites - each with it's own app space.
Your alternative is to use URL Forwarding ("normal" redirect). With this set-up, clicking the first link you gave, will display the 2nd link in the address bar. You loose the ability to mask your actual location, but it's all treated as one app space.