Installing an md-RAID during system installation creates an /etc/fstab entry
that will not work after first reboot:

/dev/md/backup /backup vfat users,gid=users,umask=0002,utf8=true 0 0 
(which is not as system, but a data partition not needed by system)

as /dev/md/backup seems not to be found after shutdown, the system refuses to
boot, tries to start emergency mode, but cannot continue. 
After booting the rescue system and commenting out above line, system boots
normally. Starting yast partitioner shows the RAID but as unused. No problem to
reedit the RAID partition data and to start the RAID then. This creates a
different /etc/fstab line:

/dev/disk/by-id/md-uuid-096b4cbe:40829716:93e25ef0:7a33b96c /backup \
vfat users,gid=users,umask=0002,utf8=true 0 0 

This is working correct after reboot. So the installer should use the
disk-by-id syntax too as it does for the "normal" partitions.

Workaround is to skip the RAID partitioning leaving the space blank and to
install the RAID after first reboot. Which will not work if you want a RAID
with system partions I fear.