Comment 16 for bug 2017929

I went and edited /boot/grub/grub.cfg directly to change the timeout in case something else in the process of updating GRUB the correct way with update-grub was a factor.

my experimentations with a full shutdown every time, in order:

timeout=0 FAIL
timeout=5 boots
timeout=0 FAIL (to confirm the error was still present)
timeout=1 FAIL
press CTRL-ALT-DEL then hit enter immediately: FAIL
press CTRL-ALT-DEL then hit enter at the 28s left mark (after 2 seconds) : boots
timeout=2 boots

It looks like GRUB needs a 2 seconds delay minimum (at least on my system) before it can load kernel -71 properly.