I'm not sure if it has been reported already (i did searched the forums, only in english tho) but the installer keeps freezing and the window becomes unresponsive when you open Show Details while the download process is happening.
It actually have happened to me with the free version too, but you maybe just overlooked this in the full release as well. I also have a customized gui on my win7 sp1 installation, it might have something to do with it, yet this never occured me once before with other installers either - nor any other programs running on my pc.

Not opening the details panel seems to help to complete the installation without glitches.