linux-boot-prober and grub on other OS

[Simon Pepping <spepping@leverkruid.eu>]

I have a debian and a ubuntu system in two different partitions on the same
disk. grub-pc on the debian system provides the boot-loader.

When I have grub-pc installed on the ubuntu system, updates of that package
overwrite debian's grub on the MBR.

When I uninstall grub-pc from ubuntu, update-grub on the debian system is no
longer able to generate good lines for ubuntu in grub.cfg.

How can I get good lines for ubuntu in debian's grub.cfg, and not overwrite the
MBR with ubuntu's grub when ubuntu's grub-pc package is updated?

Simon