westfw:
I suspect the bios doesn't like seeing two keyboards.
I tried it out. I thought I knew the answer, but I wanted to be sure. I connected two keyboards at the same time, which both work alone/independently, and they both sure worked at the same time in BIOS.
No, it's rather that BIOS is rather peculiar with keyboards and emulations etc. By far not all keyboards work in BIOS or even all ports. On a recent motherboard we acquired at work, there is ONE usb port in another color (green) which is supposed to be the BIOS keyboard port, and sure, no keyboard works in any of the other ports and, of course, not even all keyboards work in that green port...