This weekend, I received a page that one of my servers was down. I was on the way to the wedding, so I thought that I would deal with it after getting back to the condo from the wedding.
When we got to high camp at Squaw Valley, I noticed that there was a web terminal in the building where the cable car drops you off. Even though the directions on the terminal said you had it enter money, I decided to see what happened if I didn't.
When I entered the url, the web page for the site fully loaded, and then after it finished, it went to their home page. It appears that the web proxy might be modifying the http response headers to include a redirect to their web page.
It seems like this would be better if the proxy redirected the dns traffic. Or it could have just redirected traffic on certain ports.