From Fedora Project Wiki

The printable version is no longer supported and may have rendering errors. Please update your browser bookmarks and please use the default browser print function instead.

The detection of the SD slot fails if the language is not English (system language is German here). Running it with LANG=C fedora-arm-installer fixes the problem. Additionally, is there a reason why it does not use the new black root privilege login screen from Gnome 3? --TimN