Yep, did not work for me either. Has not ever worked on a Haswell NUC that I have either. Even if the NUC is connected to the network and it could get an IP with DHCP and then access the network without any proxies or such. I've always kind of ignored this and instead copied the BIO file to a USB stick and used that for the update, which works ok.
But I agree, it's annoying.
Fastboot does not disable my keyboard though, but then again I've got an OS that has USB 3.0 support. Could it be that if you're running an OS that requires Legacy USB option to be enabled, then that does not work with fast boot? I can imagine that grub or any other boot loader for example will not support a keyboard in USB 3.0 port...
Intel document about Fast Boot: