I have several multiboot systems (Arch, Fedora, Mint, Ubuntu, etc.). On each I have chosen to make Fedora the "master" distro; that is the distro that controls grub. On occasion, after a system upgrade when Fedora updates the kernel, I "lose" one of my installations -- usually Arch Linux. What I mean by "lose" is that the distro is still on the grub menu but when chosen, booting fails.
Why does this happen? Well, when Fedora updates the grub configuration...