Sorry, I have to step back. In my particular case, the problem was that I also have launched sudo update-grub on my Quantal installation. And this created a /boot/grub/grub.cfg file on my Quantal partition.
For some reasons, existing grub.cfg files on other partitions seem to completely fool the update-grub scripts on other partitions (more precise, the linux-boot-order script).
In my case, the problem was solved by removing the grub.cfg file on the Quantal partition (I still launch update-grub on my Precise partition).
I find abnormally that the mere existence of grub.cfg files on other partitions completely fool the update-grub scripts (actually, the linux-boot-prober scripts)
Sorry, I have to step back. In my particular case, the problem was that I also have launched sudo update-grub on my Quantal installation. And this created a /boot/grub/grub.cfg file on my Quantal partition.
For some reasons, existing grub.cfg files on other partitions seem to completely fool the update-grub scripts on other partitions (more precise, the linux-boot-order script).
In my case, the problem was solved by removing the grub.cfg file on the Quantal partition (I still launch update-grub on my Precise partition).
I find abnormally that the mere existence of grub.cfg files on other partitions completely fool the update-grub scripts (actually, the linux-boot-prober scripts)