When clicking items on <http://shopping.t-online.de/> they are supposed to take you to the vendor's site in a new window.
The site uses a very complicated function to open popup windows… <http://www.t-online.de/functions.js>
The problem seems to be that they pass you through a "counter" which receives the actual destination URL as an argument. When certain characters are used as part of an address it is normal to encode them in a specific way, called "escaping". The opposite process, translating the escaped characters back to normal is called "unescaping".
The other browsers ignore this. Compare the contents of the message box if you put this address into Opera and IE:
Opera escapes the string the way I would expect while IE seems to check whether the string already is escaped and actually does the equivalent of first unescaping and then escaping it.
The never ending mysteries of IE compatibility..
When the double-escaped address is sent to the server, it is not quite recognised and the server just forwards you back to the main page.
Besides IE's unexpected behaviour, it seems like the client-side and server-side programmers at T-Online do not communicate. Characters in an URI needs to be escaped server-side OR client-side, there is no point in doing both.