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When the bootloader grub shows the menu, the response to the keyboard is very
slow: about 1 response per keystroke per second. If keystrokes are entered in a
higher rate, grub stops responding requiring a reboot. Furthermore when using
the enter or right-arrow key, it must be pressed twice as grub is continuously
behind one keystroke when responding to one. This makes navigating or modifying
a menu entry extremely difficult.

Reproducible: Always

Steps to Reproduce:
1. Hook up any USB keyboard to the computer.
2. Cold or warm boot.
3. Press the down keys either slowly or quickly.
4. optionally edit a menu item.

Actual Results:  
Slowly entering keystrokes => grub is behind one keystroke with taking actions
on keystrokes and it is very hard to do something with grub menu entries
because of this (you need to constantly think of the next key press to get the
previous one acted on).
Quickly entering keystrokes => grub stops responding to the keyboard and the
reset-button needs to be used.

Expected Results:  
Menu reacts immediately when entering down arrow and choosing a menu entry by
enter or right arrow. When editing menu entries slowly keypresses are expected
to show up immediately (not one keypress later). Grub reacts normally when
quickly (faster than one per second) pressing keys and continous to act on the
keyboard.

The problem has been seen both on 42.1 and 42.2 (alfa 3).
The problem does NOT show for PS/2 keyboard (tested with Mitsumi KFKEA4SA),
only for USB keyboards (tested with Logitech G710+, Dell SK-8115, Sboard
travel).
Tested with USB 1.1, USB 2.0, with and without hub.
Interestingly: if a menu entry has a shortkey, pressing that key once will have
grub boot the OS on that menu entry without problems! Also booting the default
meny entry (not touching the keyboard) works fine.
Iirc the problem started with new hardware, probably because of the intel 6700K
and/or Asus Pro Gaming motherboard. The problem did not show up on the previous
AMD 955BE and MSI 790FX-GD70 motherboard combination.
Theme used is default.
Grub is NOT showing any faults/errors to conclude what is the problem.
The problem can be worked around by typing very slowly and thinking hard but is
very annoying!