Have checked two SLES11sp4/OES2015sp1 servers prior to upgrading, with the same result:
/etc/fstab shows device-id...which is good.
Attempted to go into 'yast2 disk' (ncurses) anyway. Clicked 'yes' to the warning.
Got the 'Initializing' message on the blue screen, but process didn't proceed any further.
Couldn't abort. Had to close ssh session.
logged back in and found '/usr/lib/YaST2/bin/y2base disk ncurses' still running.
Had to reboot machine to get rid of it after kill didn't do the job.

Looks like Partitioner is broken. These are ext3 partitioned servers.