Hello.
I'm using webproxy-test under 2.9.45 and I have a small issue with a website and probably with others.
Try visiting http://www.upc.ro when the webproxy-test is enabled and set as transparent proxy. Nothing loads up. Not the images, not the javascript, not the css and links don't work. Upon disabling the srcnat rule in the firewall (thus having direct access to the web) the website works fine.
Later edit: it seems to have an issue with the <base href=""> tag...
When the proxy is enabled I get <base href="http:///" />, while the correct tag in the page is <base href="http://www.upc.ro/" />.