Bug#655579: debian-installer: Unable to perform an installation : USB-input devices unusable
from the info you supplied (thanks!) from a previous installation it
seems the keyboard uses module hid-apple.
I have checked kernel-wedge package and that module it's already
included in the input modules  for the installer's kernel.
One thing you can try is to connect a 2nd keyboard and check if the
module it's indeed loaded when you connect the keyboard.
dmesg should recognize the keyboard when you plug it and lsmod shoud
report the module hid-apple.
Melhores cumprimentos/Best regards,