Comment # 1 on bug 994322 from Josef Reidinger

well, purpose of grub_installdevice is that it store information where grub2 is
installed as yast2 cannot detect it by itself. Reason for activate and
generic_mbr is again that yast2-bootloader read these values and show it to
user for current configuration and if user confirm setup, it redo it. So even
if something break MBR or remove 'boot' flag from disk, yast2-bootloader will
fix it. Without this file, y2-bl do not know previous setup, so cannot help
with changing existing configuration.

Currently what y2-bl do is that based on hardware setup propose to write grub2
to 
1) where lives partition for /boot/grub2/i386-pc/
2) extended_partition if /boot is on logical disk
3) where lives disk for /boot/grub2/i386-pc/

It is quite complex logic where to write, depending on many parts and can be
overwritten. So I worry that without any replacement y2-bl no longer will know
where it will be installed.

My proposel how to handle not so stable device names ( even when using udev )
is to detect such situation in y2-bl and write it to user with option to
repropose configuration from scratch.