Comment # 9 on bug 1200983 from Michael Hirmke

I suppose it is a kernel issue.
It also happens in init level 3, but for the keyboard it is a bit different
than for the mouse:

1. During boot the keyboard is usable as expected - one can chose the kernel to
boot, enter the LUKS passphrase and so on.
2. As soon as the system is up, the keyboard lights go off.
3. The next keypress is ignored then.
4. After the second keypress the keyborad lights go on and one can use the
keyboard again.
5. After a few seconds without keyboard usage the lights are switched off again
and we restart at no 3.

Unplugging the keyboard and plugging it in again solves this problem. From then
on the keyboard is working as expected.

As for the mouse: It doesn't work at all until it is unplugged an plugged in
again.