Is it possible it's not the case?
I've noticed that, depending on which keyboard I use and which USB ports (plugged directly into the back of the computer, not into the case or a hub) I use, the KB doesn't always register fast enough for me to press the BIOS/boot menu shortcut keys.
On my machine with my current keyboard, it only worked right plugged into the USB3 ports on the back of the motherboard, but not the hub plugged into the same port. It doesn't work on the USB2 ports at all. The last build I did for somebody else, it was the opposite - the USB2 ports were the "reliable" ones.
I've chalked it up to voodoo.