grub2 help needed

["Juan R. de Silva" <juan.r.d.silva@gmail.com>]

I'm fairly new to GRUB2, thus need help to understand it better.

I've created a new partition on my HD and installed Ubuntu Natty on it. I 
wanted the Squeeze GRUB to be in charge and installed Natty GRUB to its 
own root. I intended then to make Squeeze GRUB to find the new OS and add 
it to its menu.

I booted into Squeeze and run 

'os-prober & update-grub'

GRUB did not find newly installed OS.

Then I tried to reinstall GRUB by running 

'grub-install --recheck /dev/sda'

Still no results.

Finally I mounted Natty / and then run again 

'os-prober & update-grub'

To my surprise this time GRUB succeeded to find Natty and added it to the 
Squeeze GRUB menu.

Isn't it a faulty/buggy behaviour? Wasn't GRUB or os-prober supposed to 
find newly installed OS without it's root being mounted first? Or I 
misunderstand something here?

Thanks in advance.