grub2 password prompt every boot/reboot

[martywd]

1)Release: Linux Mint 15 "olivia" Edition: MATE 64-bit
2)Config grub2 to password protect editing entries in the grub2 boot menu.
In file: /etc/grub.d/40_custom
I added the following:

  set superusers="user1"
  password_pbkdf2 user1 grub.pbkdf2.sha512.10000.84773E6389CE4F7...E61E89E047.....

3)What happens: On every boot/reboot, after waiting for the configured grub menu delay and _without_ pressing any key(s), I get an 'Enter Username/Enter password' prompt halting further booting to Desktop login. Once configured username and password are entered the boot continues to the Desktop logon screen.
4)Expected: Prompt for user/password _only_when_ 'e' or 'c' key press is initiated in the grub2 menu.
5)Problem happens: Always (configured as noted above).

grub2 packages intalled:
 grub-common 2.00-13ubuntu3
 grub-gfxpayload-lists 0.6
 grub-pc 2.00-13ubuntu3
 grub-pc-bin 2.00-13ubuntu3
 grub2-common 2.00-13ubuntu3
 grub2-theme-mint 1.0.9