I have the same problem in 13.10 with the default grub setup: it ignores Shift and just starts the newest installed kernel. It also doesn't show the menu on restart after a crash, which would be a big problem if a newly-installed kernel (or https://wiki.ubuntu.com/Kernel/MainlineBuilds test kernel) turned out to be unbootable.
Workaround: comment out GRUB_HIDDEN_TIMEOUT=0 in /etc/default/grub to always display the boot menu.
I have the same problem in 13.10 with the default grub setup: it ignores Shift and just starts the newest installed kernel. It also doesn't show the menu on restart after a crash, which would be a big problem if a newly-installed kernel (or https:/ /wiki.ubuntu. com/Kernel/ MainlineBuilds test kernel) turned out to be unbootable.
Workaround: comment out GRUB_HIDDEN_ TIMEOUT= 0 in /etc/default/grub to always display the boot menu.