So a friend got stuck as well at the authorisation page. Nothing happened after he authorised the payment. Well, he called his bank today and asked if there was an issue with his card and they told him, the website didn't support 3D-Secure for authorisation. Apparently, they were able to confirm this after looking into their system in order to find out what went wrong.
If this really is the case, then they royally screwed up. It sounds like the channel back from authorisation to the website didn't work, which could explain the unusually high number of complaints about people failing at that stage.