This is the classic bug. Since 2.6.35-gentoo-r10 came out I found out that if I launch grub-mkconf -r9 will come first in the list than -r10 If you have default 0 or whatever: the previous default value will be wrong. Solution: -10 should come before -9 in the list so that default # don't ever need to change.
I can confirm this.
bug reports go upstream for grub2