Comment # 4 on bug 960517 from Michael Chang

(In reply to Jiri Srain from comment #3)
> Michael, did I miss anything?

No. You didn't.

I'd also like to add that 13.1 and Tumbleweed are different grub2 versions
(2.00 and 2.02-beta2) so that if you upgrade without reinstalling mbr to purge
out-dated embedded core.img with new one, the ABI mismatch will occur between
core.img (from 13.1) and modules (/boot/grub2/i386-pc/*.mod from Tumbleweed)
and system dies if you reboot.

You either have to install generic mbr to use volume boot record, like:

 dd if=/usr/lib/boot/master-boot-code of=/dev/vda bs=440 count=1
 update-bootloader --reinit (make sure volume boot record updates with latest
blocklist address of core.img)

Or modify your /etc/default/grub to contain only mbr device
(hd0)

Of course, you can also use YaST bootloader to change the loader location from
boot partition to disk's mbr.

Thanks