Solution: Either remove the network cable and restart or Go out for lunch and enjoy (it takes ages, 2-3 hours for the whole installation for big networks).
This is a very common problem that occurs often in presence of huge networks (global corporate networks are good candidates); the reason why it all happens seems to be related to some domain resolutions. The installation runs smoothly to this point, then it appears to hang for a long time, so long the temptation cancel the installation is almost irresistible. What stops you from doing it is obviously the fact that from taskmanager everything seems to be just fine. If you let it be for a couple of hours it evetually will finish the installation alright. I am at the moment not aware of other solutions rather than disconnect the machine from the network or - my favourite - go out for lunch, and make sure to have a big one.